Had same error, tried all suggestions, but here is the one that worked for my iPad . Delete the history by double clicking the button on face of pad to bring up history of used apps which will show at very bottom. Hold finger on app until they all jiggle and then touch the circled minus (-) on each app. It only removes the app history, it does no harm. Good luck
I am having repeatedly the same problem with my iPhone 4. Deleting the history seems to work most of the time, but let's hope Skype gets to grip with the underlying problem and gives us a fix soon! It is driving me mad!