SYSTEM call from trigger error

We are using Informix On-Line 7.20.UC3 and have a simple trigger on a table that fires after an insert. During the trigger, we build a string that contains a path to an external .4ge program. So far, so good, this has been working for months. But now, we get this error from the trigger trace: exception : looking for handler SQL error = -668 ISAM error = -172 error string = = ""exception : no appropriate handler Using finderr on the numbers doesn't give much help. ------------------------- -668 System command cannot be executed. A system call failed in the operating system. The following example shows a statement that might cause an error: SYSTEM 'hello'; ------------------------ So, it seems that the trigger can't find the executable. But, the path statement is fine (it is a full path). The directory tree has no permission problems and if we execute the external from the shell it works fine. ----------------------- -172 ISAM error: Unexpected internal error. --------------------- The online.log file shows nothing. Any clues? The mysterious part is that everything was working and nothing (as far as the external program) was changed.