Deserializing a struct with SoapFormatter

Question

I added a new member to an existing class that's serialized. The SoapFormatter was used on released versions, so this can't be changed. The main problem is deserializing old versions that don't have this new member.

The new problem is when ISerializable is added to the class, structs in that class can no longer be deserialized. I get the exception message: "Top object cannot be instantiated for element foreColor". (foreColor is a System.Drawing.Color).

How can I get the SoapFormatter to read both old and new versions, and still handle structs?

Thanks!