I can't seem to connect to your server through FTP anymore.
I don't think that error is the cause of the problem, seems more like a result of the image upload failing in the first place.
The issue is the session is freezing and that doesn't have an error associated with it. I don't know where to go from here. I could update the page to not use sessions and that might be an acceptable work around.
Another solution might be to go to another hosting provider that can configure their server properly and be more helpful when there are issues. Even if you got a test account on another server and demonstrated it worked on that one it might open their eyes and accept it is their issue.