iCloud there was a problem completing the backup

After I installed the iOS5 on my iPad 2, I got this error message: "There was a problem completing the backup." while completing a back-up to iCloud. I tried hard reset, reset network, and erase all contents, but the problem is still there. I was able to get my iPhone 4 to complete the back-up with iCloud.To fix the "iCloud backup failed" issue, you have to plug the iPad to your PC, and enable