Blank crop_process in Avatars Plugin, WPmu 2.7

Hi all, first off, I'd like to congratulate the staff here at wpmudev for a great service, you guys rock!

I have a problem with the avatars plugin, I followed all the installation instructions correctly, updated to the brand new version 3.2.0 and the problem is still the same.

I can access the upload Blog/User avatar screen, I choose the file to upload, then I load the Crop screen, I click Crop Image, and then It loads:

However, this page loads blank, the top admin bar, also loads blank! Here is a screen shot of the problem:

I just checked my .htaccess and httpd.ini, and both have the Avatar Rewrite rule: RewriteRule ^(.*/)?avatar/(.*) wp-content/avatar.php?file=$2 [L]

The directory in wp-content/avatars is created, and the image is uploaded, however, it is not cropped and saved in different sizes as it should be, and none of the previous images are deleted.

I must mention that the server is a Windows Server 2003 with ISAPI 3 Rewrite engine, is this a problem?

Thanks in advance for your help!