Yikes! "Error 0"

I hate it when this happens. Using 4GL v4.00, I'm trying to recompile into .4go a .4gl program that was originally compiled as .4ge. It's about 85K, so I can't say I've been over it with a fine-toothed comb, but the code looks correct. Upon trying to compile, either from within the RDS or using "fglpc" from the shell, I get the message: "Error 0. I/O error while running fglc." The .err file that is written is incomplete; it stops about 1/3 of the way through the code. Commenting out the function in which the compilation stops doesn't help; the compilation bombs after another 40 lines. There is no similarity between the place the original compilation ends and the second compilation ends: the former stops after a PROMPT and and IF, the second after a CONSTRUCT, so it doesn't look like the code at the tail end of the .err is at fault. Anyone know what might be causing these errors? They're driving me crazy! -- --Dave--