Matrix: Why do I get error "...GPSF 906..." when trying to apply changes?

After an upgrade from ECS to EHX V11, when I tried to apply changes I got the error message below.

In this particular case, the reason for this error message was because the "Control Identifier Seed" values for many of the telephone controls were equal to 9, see below.  After manually changing to some other unique value, the error was gone and I was able to apply changes.