Avatar Issue

I have installed the avatars plugin. The blog avatar works perfectly. However, I'm having issues with the user avatar. When I select Users/Your Avatar, the correct page is displayed. I browse and select an avatar. But in using both the 'Upload' and 'Alternative Upload' I receive the message:

"Cannot load user-avatar."

the url after the error with alt upload:
<site>/users.php?page=user-avatar&action=upload_process

any thoughts?