Cannot open file 'netsrv.iem'

Hello, We are currently running Informix Dynamic Server 7.2 on an HP9000 K250 series 800. We have owned the system for over a year now but recently we have had more users logging into it. When the systems reaches about 120 users, and this is never certain, it may be 110 users, it may be 130 users, but we periodically obtain the following message from our 4GL programs: Program stopped at "sumcut_list.4gl", line number 74. 4GL run-time error number -25588 Cannot open file 'netsrv.iem'. Relating the line number to the source code reveals the line LET f_mode = "S" this is the first command after the DEFINES section of the MAIN function of the program. I think we have a resource problem on the machine but I am struggling to put my finger on exactly what is causing it. Is it a Unix kernel problem, or is it a onconfig problem? I would be very grateful if anybody has experienced the same sort of problems that we are experiencing could show me the light, so to speak. Regards, Paul Wheeler.