I recently converted my vBulletin forum to xenforo and just ran into a problem uploading avatars. I've tried changing folder permissions to 755 or 777, but it did not work. PHP scripts are owned on the server by the account user.
I've also looked into error logs and noticed this kinda error for some users:
getimagesize(/home/tgg/public_html/forums/data/avatars/l/11/11065.jpg): failed to open stream: No such file or directory Today at 10:11 AM - library/XenForo/Model/Avatar.php:252
When I tried to upload, there was no server error at all.