asp.net ajax client-side framework failed to load.

I got an error saying that "asp.net ajax client-side framework failed to load."

But it was working fine yesterday.Even code reverting didn't work for me.Then I found .Net 3.5 SP1 in my Control Panel - Add/Remove Programs. I clicked Change... and was relieved to see a "Repair" option.

With bated breath I waited for Windows to complete the repair. After a few minutes, I saw that the repair was complete. Now for the test. I ran my web application and all of the Ajax errors disappeared.

Perhaps this was coincidental; who knows. I suppose I could go through my logs, but I'm back in business and that is good enough for me. Of course, this doesn't explain how Ajax got broken in the first place.