Stefano, Charlie and Trex - thanx for your suggestions. Looking at the errors in /var/log/messages, I see a number of missing files that my application was looking for - they were all in /var/lib/php4. It appears that my app has this library hard coded somewhere.
I took a 7.6 server, copied the files over but still nothing. Further investigation tells me that there are a number of php4 commands that are "depreciated" - it appears that missing libraries are not my only issue.
Maybe it's time for a phpnuke upgrade as well.
Thanx again.