I'm using the 'Continuus' version control software and building from within this environment using 'object make'to call the C51 compiler v5.50. I have a problem that half way through the build, windows (NT4.0) pops up an error dialog which reads : "16 bit MS-DOS Subsystem" "C:\WINNT\system\cmd.exe" "The NTVDM CPU has encountered an illegal instruction." "CS:fe2e IP:010a OP:8f 9f 8e ad 24" Building on a different machine doesn't produce the problem. Building under Nmake doesn't produce the problem. I don't know whether the problem is with the compiler, the make utility or Windows (NT4). Can anyone suggest anything? - Dave