DFS2403I DYNAMIC UNALLOCATE RC=rc ERROR
or
Explanation
IMS issued an ALLOCATE or UNALLOCATE command for a SYSABEND or SYSUDUMP data set. Either a nonzero return code or a nonzero information code was returned by SVC 99.
If RC=04, Error Code=0254 is returned by SVC 99, you requested conditional ENQUEUE on a resource that is currently unavailable. One reason for getting this return and error code would be issuing an IMS MODIFY command while a mount for a log is pending.
System action
IMS continues execution (it might be in abnormal termination processing).
Programmer response
Contact the z/OS® system programmer.