CASTM5024S Signon SAF error: user ID user-identifier, group security-group at LU logical-unit

A user tried to signon using TM with ID user-identifier, specifying secruity group security-group from logical unit logical-unit. The signon was rejected because of a SAF error. An unexpected external security system error was returned on the verify call.
System Action:
The user signon is rejected.
Resolution:
Notify security personell.
Module:
castmc
Destination:
Console