exec() problems - addedum

I forgot to mention this: i'm running php4.0.1pl2, zend optimizer, rh6.2 I'm having trouble getting the output of a program using exec(). Instead of the expected output (and the output I get using the exact same commandline in the shell) I get no ouput at all and a return value of 11 (the third parameter of the exec() function). It's not a permission issue: with some parameters the call does work and I get the expected output. I tried popen, I tried $cmdline - it just won't work... What does a return code of 11 mean ? I looked at the source of the program and there is no exit(11). I would appreciate any feedback on this - it's driving me crazy :-(