Problem with exec(). Help needed!

I'm using PHP for accessing PROGRESS database. Due to lack of native interface between PHP and PROGRESS i'm forced to get the data like this: ......some code...... exec($_pro . ' -U '.$p_usertext.' -P '.$p_passtext.' -p query.p',$pro_out,$pro_code); ......some code...... where -> $_pro is a string containing calling parameters for PROGRESS console client (they call it char client), -> query.p is a PROGRESS 4GL script doing actual query and returning to stdout some data in the form '$variable=value;' so it can be eval()'d in PHP. The problem appears when i dynamically compose some PROGRESS 4GL script in PHP string then writing it to a file and then exec() above mentioned sequence. PROGRESS works just fine - when i start its client app from pure command line it returns all the data it should. BUT same script but called from PHP via exec() -- PHP hangs and i'm restarting Apache to get it working again. If i simply comment out the line with exec() - all works fine again (of course without the data from PROGRESS). Configuration of server: pentium III 500MHz with 384 MB of RAM / Windows 2000 Server SP3 (Russian). Apache 1.3.26 + PHP 4.3.0 (module, not CGI) our project has only 3 users at this time, so this hardware is powerful enough :).