This is an annoying asp.net message I believe. Instead of saying something like "page moved". But, to the point, for a "regular joe" (non programmer) Windows 7 user like me who gets this error all the time, the answer is even more nebulous:
https://support.microsoft.com/en-us/kb/888418
The article does a lot of explaining (more for page developers it seems), but if it's not a nuisance, the article says you can wait for the update to .net fx 1.1 (which I assume is out a long time ago? and would be part of windows updates). The article also says that if it's something you actually need fixed now (like you see this about 15 times a day while browsing), you can "contact microsoft for the hotfix"?? But why write an article and not include the hotfix for those who need it? Contact us page basically takes you nowhere. You also don't provide the link to the .net fx 1.1 updated version? I'm a little confused. Oh, and after I downloaded the dotnetfx.exe, the exe file shows as a pdf icon? Turns out that's another hotfix, impossible to find.