Autodesk 3ds Max Failed Error 20

Hello all,
I can’t find out why this following error message occurs, "The software license check out failed; error 20" (attached image). I made attempt in several ways such as by deleting autodesk files, FLEXnet files, and uninstall-install 5 times.
But all goes to fail. It displays repeatedly. Need any solutions to solve this problem.
Autodesk 3ds Max 2011
The software license checks out failed Error 20.

Thanks for suggestions.
