Out of memory error when adding an imagefield to a content type

Hi, I'm getting an out of memory error when I add an Imagefield to a content type. I created a new content type, and using CCK I added an Imagefield. Immediately the site broke with an out of memory error:

Fatal error: Out of memory (allocated 35913728) (tried to allocate 1672436 bytes) in /home/sites/theillustrationgallery.com/public_html/includes/bootstrap.inc on line 634

I've tried it a few times, and it breaks each time. I have to reinstall the database from a backup to get it working again.

I don't think it can actually be running out of memory, as I've allocated 250mb in php.ini

Any ideas on what's going on?

Thanks