I recently had a client experience this issue after upgrading to 7.5.4. Whenever they would try to insert a new Account and Contact or Contact into the system they would receive “Void Sage.Entity.Interfaces.IContact.set_GlobalSyncID(System.Nullable ‘1)” as an error when they tried to save the new record. The record did save but the screen would not navigate away from the insert screen.
It turned out the issue was that the Contact entity has had several new properties introduced in 7.5.4. One of these is called GlabalSyncID. In their system after upgrading these entity properties were not included in the entity model. I went ahead and added all of the missing standard 7.5.4 entity model properties. It is important to note when adding the properties the system will not automatically define the properties as the correct types. You need to make sure to redefine the types after adding them to the entity model.
The following proprties need to have their types re-defined once added: