Running out of mem on build?

My sitemap for my high traffic forum at http://forums.pcapex.com is no longer making new sitemaps. it worked great for about a month but ever since then it no longer makes new site maps. When I did a manual run, after a long time (15 - 25 min) I get an error page that says the script ran out of memeory. I have upped the PHP memory limit to 32MB and then to 48MB and still the same thing happened. Any ideas?

I have the exact same setup running at http://forums.gameapex.com flawlessly.

Thanks!

Try less URLs per file maybe?

That's so simple it might just work! I'll give that a shot.