[Plugin: WordPress Mobile Pack] Image Resizing breaks

I’m running:
Wordpress 3.0.1
PHP 5.2.11
with GD bundled 2.0.34.
IIS 6.

If I turn on the image resizing feature, any pages with images to be resized fail to load. Eventually the phone shows an error 504 message (Gateway timeout).

I’ve checked that the cache folder is writable, but no images are ever written to it.

I’ve tried disabling other plugins, so I’m pretty confident it’s not a plugin conflict. I’m stuck and would appreciate any help you could provide.

Thanks!