Apache 2.0.50 generates drwatson errors

I have an apache 2.0.50 installation, with PHP 5.1.2. It was working
fine, until I increased the RAM used by PHP from 8M to 32M (I have 1G in
the box, and no other apps running). It's w2k SP4.

There is no information in the logs except:
[Thu Apr 13 17:47:29 2006] [notice] Parent: child process exited with
status 3221225725 -- Restarting.

This occurs whenever I run a PHP script that uses a little more memory
than previously.

Any thoughts as to the root cause ?

I have upgraded to apache 2.0.55, to no avail.

Ian