New build of control cannot deserialize the property of elder built?

Hello, I've developed a custom control which contains a property of type Collection (Which is a custom collection derived from CollecionBase). Everything is ok normally, I put this control onto a form, change it's properties, including the collection, build the project, close the solution, re-open, etc... But when I make a change in my control and rebuild it things get change...When I open the project that I use the control, I get an error stating this : Object type cannot be converted to target type It seems that somehow the serialized collection property could not be restored back...But I don't do any change in the collection class in my new build which may reflect the serialization? Anyone has any idea? Best Regards, Özden

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