Base class defines get_Item or set_Item, cannot create expando class. Methods reserved for the expando fields.
An expando class extends a base class with a member named get_Item or set_Item. This is not allowed because it leads to a conflict with the get_Item or set_Item properties implicitly defined for expando classes.
To correct this error
Rename the base class member named get_Item or set_Item.
Do not inherit from the base class.
Remove the expando modifier from the class definition.