Any suggestions for debug environments?

This is probably a PHP question rather than WordPress, but I thought I’d try here.

I’m trying to debug a problem that appears with a particular theme and plugin (see https://www.ads-software.com/support/topic/147667?replies=1).

In some cases, I do get an entry in the error log: “premature end of script headers: php5.cgi”. I also get a file named “core” created in the root of the web site.

It’s been a l-o-o-n-g time since I used a debugger to step through code — for my PHP work, it’s been sufficient to scatter echo statements when I was having problems but this strategy isn’t helping to shed any light here.

Can anyone point me to the info on how to set up a debug scaffold so I can see exactly where WordPress is crashing? (I don’t expect to be able to solve the problem, but maybe I can ask a more intelligent question.)