I faced same issue, which is now resolved for me.
I went to http://testng.org/doc/download.html , here a link is displayed from which you can check old plug-in versions of TestNG, clicking that will take you to http://beust.com/eclipse-old/ , this page displays list of urls. I selected a version below to latest one and copy pasted that url to Location field in Eclipse and it worked !!!
Hope it helps…