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Open the Registry Editor (Search for Registry Editor in the Window search)
Select the Edit > Find (Ctrl+F) and write down the name of the plugin: Unreal Datasmith Exporter for 3ds Max
Select the associated Registry Key folder on the left and delete it.
Search again for Unreal Datasmith Exporter for 3ds Max to ensure nothing else is found.
Then make sure to delete DatasmithMax202X.dle and Startup - UnrealStudio_Datasmith_Attributes_Holder_Modifier.ms in the following locations
C:\Program Files\Autodesk\3ds Max 202X\Plugins - DatasmithMax202X.dle (File)
C:\Program Files\Autodesk\3ds Max 202X\scripts\Startup - UnrealStudio_Datasmith_Attributes_Holder_Modifier.ms (File)
You can then try to install the plugin again.
If these steps did not help resolve the errors. Please report a bug and provide the log file when submitting the form - Refer to this article on how to get the log file: