MSIR.0417 New exception value (value) for (field) matches a format and so can't be added after records have been added to the file

This message indicates that a SIRFIELD FORMAT or RELATE command was issued for field 'field' with an EXCEPTIONS clause containing 'value', and that the command could not succeed because it matches the primary format, an alternate format, or the error format, but records have been added to the file.

Exception values which match a format can only be defined before records are added to the file. This is a very rare error message; if you receive it you should review the use of format-matching values as exception values, as discussed in the Sir2000 Field Migration Facility Reference Manual. If you wish to define 'value' as an exception value for 'field', you must re-INITIALIZE the file and re-execute the series of SIRFIELD commands for the file. 

The command is rejected.