Troubleshooting PHP support

Hi all,

I'm attempting to get PHP working with Aolserver 4.5 as a workaround  
in a time crunch here. OS is RHEL 4. I compiled PHP5 in a VM that is  
basically identical to my production server and it worked like a  
charm. On the production box, however, the script produces no output  
and the response headers say "500 internal server error". There is  
nothing in the error log (debugging turned on). For the sake of it, I  
tried PHP4; again, it compiled just fine and loads OK at server  
startup but no output. This time I got a "200 OK" message in the  
response headers, though. Nothing in the logs again.

Can anyone give me some pointers on how to troubleshoot this?

Thanks in advance.

Michael