Edited Issue: Assign an Enum to an object type property in a Propertygrid [20036]

Fixed in v2.1.

In the meantime, you can go in PropertyGrid/Implementation/DescriptorPropertyDefinitionBase.UpdateAdvanceOptionsForItem method and replace this line :
if( markupProperty != null )
with this line :
if( (markupProperty != null) && (markupProperty.PropertyType != typeof(object)) )