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Attribute '<attributename>' cannot be applied multiple times

The attribute can only be applied once. The AttributeUsage attribute determines whether an attribute can be applied more than once.

Error ID: BC30663

To correct this error

  1. Make sure the attribute is only applied once.

  2. If you are using custom attributes you developed, consider changing their AttributeUsage attribute to allow multiple attribute usage, as with the following example.

    <AttributeUsage(AllowMultiple := True)>