Problem: On the Search results page you have the Search Action Links to display the sort options. Whenever you click on the field to sort on it gives you a Javascript.
Resolution: Make sure your Search box is on the Search Results page.
If you have customized Master Page make sure that you are displaying the Search box. Even if it is hidden you will get the Javascript error. If it is deleted please insert the web part back on the page.
Not sure how the sort by is tied with Search Box web part. 🙂
Ameet Phadnis Technical Blog 
Ambar
March 22, 2012 at 10:17 pm
This javascript error is also coming for the “Show more” / “Show less’ links inside the Search Refinement Panel web part.
Make sure that you have the Search Box [web part] on results page also..
Manas
June 21, 2012 at 12:50 pm
Thanks man… Thanks a lot .. u made my day…