Hey Gytis,
Thanks for the quick response 
Just errors related to Dev work, e.g. a modified query which contains an error, or a violation of a primary key, etc. Like I said, it's not something which happens regularly.
To replicate in a test environment, update the SU_NUMBER_ALLOC table to set the NUMBER_ALLOC value for CL_CALL_LOGGING to a call number which already exists. If you then create a new Call, a primary key violation occurs and you see "Violation of PRIMARY KEY constraint 'CL_CALL_LOGGING_PK'. Cannot insert duplicate key in object (etc)".
Whilst the error message is good for troubleshooting, I can get it via Event Viewer or running dbgview rather than via the customer.
Cheers,
Al.