If you are here, then you are facing this problem right now. I hope I can help you with the issue.
What you need to do is add the jQueryMobile reference to your application, it should be a line like below:
Note: You can find Microsoft Ajax Content Delivery Network (CDN) here.
If you have your reference in place but you are still getting this error message;
b) CDN might be temporarily unavailable, try with a local copy of the .js file.
If you are using a local copy of .js file and getting this error then check the .js file for any syntax errors. Have you changed anything in the file?
Hope this helps someone.