{"id":14367,"date":"2026-06-08T17:25:41","date_gmt":"2026-06-08T15:25:41","guid":{"rendered":"https:\/\/store.algosyntax.com\/?post_type=asx-lms-tutorial-cpt&p=14367"},"modified":"2026-06-08T18:06:07","modified_gmt":"2026-06-08T16:06:07","slug":"widget-blueprint-could-not-be-loaded-because-it-derives-from-an-invalid-class-fix-unreal-engine","status":"publish","type":"asx-lms-tutorial-cpt","link":"https:\/\/store.algosyntax.com\/tutorials\/unreal-engine\/widget-blueprint-could-not-be-loaded-because-it-derives-from-an-invalid-class-fix-unreal-engine\/","title":{"rendered":"Widget Blueprint could not be loaded because it derives from an invalid class| Fix | Unreal Engine"},"content":{"rendered":"\t\t
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Unreal Engine may sometimes show this error when opening a Widget Blueprint:<\/p>

Widget Blueprint could not be loaded because it derives from an invalid class.\nCheck to make sure the parent class for this blueprint hasn't been removed!<\/code><\/pre>
This usually means the Blueprint is still trying to inherit from a class that Unreal can no longer find.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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What causes this error?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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The most common cause is renaming a C++ class without adding a Core Redirect.<\/p>
However, this is not limited to simple class renames. Moving a class to another module can cause the same issue, because the full Unreal class path changes.

This can happen when:<\/p>
  1. A C++ class is renamed.<\/li>
  2. A class is moved to another module.<\/li>
  3. A class is moved from project code into a plugin.<\/li>
  4. A class is moved between plugin modules.<\/li>
  5. A plugin or module is renamed.<\/li><\/ol>
    For a visual example,\u00a0 watch the video on this page.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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    Symptoms<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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    You may see the popup when opening a Widget Blueprint:<\/p>
    Widget Blueprint could not be loaded because it derives from an invalid class.\nCheck to make sure the parent class for this blueprint hasn't been removed!<\/code><\/pre>
    Other symptoms may include:<\/p>
    • The Widget Blueprint will not open.<\/li>
    • The parent class shows as invalid.<\/li>
    • The Blueprint cannot compile.<\/li>
    • Other dependent Blueprints may also fail to load.<\/li>
    • Packaging or cooking may fail because Unreal cannot resolve the missing class.<\/li><\/ul>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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      How to fix it<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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      To fix the issue, you need to add a Core Redirect.<\/p>
      A Core Redirect<\/strong> tells Unreal:<\/p>
      When something asks for the old class, use the new class instead.<\/code><\/pre>
      The fix has two parts:<\/p>
      1. Find the old class name.<\/li>
      2. Redirect it to the new class name.<\/li><\/ol>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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        Step 1: Identify the old class name<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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        Right after the popup appears, open the Output Log.<\/p>
        In Unreal Engine, go to:<\/p>
        Window > Output Log<\/code><\/pre>
        Search for the name of the broken Blueprint.

        You can follow what happens in the video if it makes it easier for you but<\/p>
        You are looking for a message similar to this:<\/p>
        CreateExport: Failed to load Class X as Parent<\/code><\/pre>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t
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        X here is the class name Unreal is still trying to load from the Blueprint asset.<\/p>
        Watch the video for the exact Output Log search process. It will make it easier.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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        Step 2: Identify the new class name<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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        Next, identify the class that should replace the old one.<\/p>
        Usually, this is the class you renamed or moved the old class into.<\/p>
        For native C++ classes, the reflected Unreal class path usually looks like this:<\/p>
        \/Script\/ModuleName.ClassName<\/code><\/pre>
        Do not include the C++ prefix unless it is actually part of the reflected name.

        <\/p>
        For example, a C++ class named:<\/p>
        UAxGridChildWidget<\/code><\/pre>
        is usually referenced by Unreal as:<\/p>
        AxGridChildWidget<\/code><\/pre>
        not:<\/p>
        UAxGridChildWidget<\/code><\/pre>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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        Step 3: Choose The File To Add Core Redirect in<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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        The CoreRedirects we’re talking about are added in Configuration files ending in .ini extension.
        This file is located :<\/p>
        At the project level, The redirect is added in:<\/p>
        Config\/DefaultEngine.ini<\/code><\/pre>
        If the class belongs to a plugin, you can place the redirect in the plugin config file.<\/p>
        For a plugin, create an .ini<\/code> file that matches the default plugin config name, for example:<\/p>
        Plugins\/YourPlugin\/Config\/DefaultYourPlugin.ini<\/code><\/pre>
        Then add the following redirect:<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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        Step 3: Add The redirect in the config file<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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        Use this format:<\/p>
        [CoreRedirects]<\/span>\n+ClassRedirects=(OldName=\"OldName\",NewName=\"\/Script\/NewModule.NewName\")<\/code><\/pre>
        For the Output Log example above, the redirect would look like this:<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t
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        \n\t\t\t\t\n\t\t\t\t\t[CoreRedirects]\n+ClassRedirects=(OldName=\"\/Script\/EnhancedUIGrids.AxLineGridChildWidget\",NewName=\"\/Script\/EnhancedUIGrids.AxGridChildWidget\")<\/xmp>\n\t\t\t\t<\/code>\n\t\t\t<\/pre>\n\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-b9c5c97 e-flex e-con-boxed e-con e-parent\" data-id=\"b9c5c97\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-0ed31ad elementor-widget elementor-widget-heading\" data-id=\"0ed31ad\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Final steps<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5a72c22 elementor-widget elementor-widget-text-editor\" data-id=\"5a72c22\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>\u00a0After adding the redirect:<\/p><ol start=\"1\" data-spread=\"false\"><li>Restart Unreal Engine.<\/li><li>Open the broken Blueprint.<\/li><li>Compile it.<\/li><li>Save it.<\/li><li>Check the Output Log again for any additional missing classes.<\/li><\/ol><p>Sometimes one broken Blueprint may reference multiple renamed or moved classes. Fix the first missing class, restart, then repeat the process if another missing class appears.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-a5fb38f e-flex e-con-boxed e-con e-parent\" data-id=\"a5fb38f\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-091bfce elementor-widget elementor-widget-heading\" data-id=\"091bfce\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Related tutorial<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-da51b4e elementor-widget elementor-widget-text-editor\" data-id=\"da51b4e\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"isSelectedEnd\">For more information about Core Redirects and moving Unreal Engine content or classes, see this related tutorial:<\/p><p><a href=\"https:\/\/store.algosyntax.com\/tutorials\/unreal-engine\/ue5-moving-content-and-classes-to-another-class\/\">UE5: Core Redirects In Unreal Engine<\/a><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"featured_media":0,"template":"","asx-lms-tutorial-categories":[86,142,58,45],"asx-lms-tutorial-tags":[143,46],"class_list":["post-14367","asx-lms-tutorial-cpt","type-asx-lms-tutorial-cpt","status-publish","hentry","asx-lms-tutorial-categories-unreal-api","asx-lms-tutorial-categories-blueprints","asx-lms-tutorial-categories-unreal-c-api","asx-lms-tutorial-categories-unreal-engine","asx-lms-tutorial-tags-blueprints","asx-lms-tutorial-tags-cpp","entry"],"acf":[],"_links":{"self":[{"href":"https:\/\/store.algosyntax.com\/asx-rest\/wp\/v2\/asx-lms-tutorial-cpt\/14367","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/store.algosyntax.com\/asx-rest\/wp\/v2\/asx-lms-tutorial-cpt"}],"about":[{"href":"https:\/\/store.algosyntax.com\/asx-rest\/wp\/v2\/types\/asx-lms-tutorial-cpt"}],"version-history":[{"count":2,"href":"https:\/\/store.algosyntax.com\/asx-rest\/wp\/v2\/asx-lms-tutorial-cpt\/14367\/revisions"}],"predecessor-version":[{"id":14385,"href":"https:\/\/store.algosyntax.com\/asx-rest\/wp\/v2\/asx-lms-tutorial-cpt\/14367\/revisions\/14385"}],"wp:attachment":[{"href":"https:\/\/store.algosyntax.com\/asx-rest\/wp\/v2\/media?parent=14367"}],"wp:term":[{"taxonomy":"asx-lms-tutorial-categories","embeddable":true,"href":"https:\/\/store.algosyntax.com\/asx-rest\/wp\/v2\/asx-lms-tutorial-categories?post=14367"},{"taxonomy":"asx-lms-tutorial-tags","embeddable":true,"href":"https:\/\/store.algosyntax.com\/asx-rest\/wp\/v2\/asx-lms-tutorial-tags?post=14367"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}