Itunes won't back up my iPone because an error occurred!

I have an iPhone 4s 16GB.I want to back it up on to my computer,because,soon I will be getting the 5s and I want to have everything one there.

But iTunes keeps saying "iTunes could not back up *****'s iPhone because an error occured.I've tried everything but nothing seems to work.No way am I taking the risk of resotring my 4s,though.

I would really appreciate it if someone helped me!

Thanks!