This error indicates O/S lack of resources due to heavy load on the system. Clients usually when trying to connect recieve ORA-12518: TNS:listener could not hand off client connection which is an other idication for lacking of resources, cause listener cannot open the required server process/thread to handle the new conenction request.
DB alert.log should have similiar entries to the follwoing :
Error: skgmattach - Unable to register map, error 4210
ORA-00600: internal error code, arguments: [ksmlsge1], , , , , , ,  ORA-27103: internal error OSD-00013: Message 13 not found; product=RDBMS; facility=SOSD