Frame connection is missing its reference collection.
Frame connections are related to their supported members and supporting member via the reference collection. These relationships exist as specific types of relationships; however, a relationship exists to the Frame Connection across an unknown relationship.
A custom frame connection was developed using an incorrect relationship between the member system and the frame connection reference collection.
Another possible cause for this error is if the frame connections were migrated from Version 4.0 of the software. In Version 4.0, more general relations were being used between the frame connection and the member systems. These relations, however, were converted to more specific relations in Version 4.1. It is possible the version migration did not convert these relations properly.
The frame connection will not compute properly when the member system is manipulated.
What You Should Do
Hexagon PPM will need to review the data to see what the unknown relation is.
Ask your database administrator to back up the model.
Send the database backup to Hexagon PPM Support.