It is possible that the correct .NET framework is already installed, and the installer has nothing more to do.
You can check quite easily, but you need IE (if definitely doesn't work in Chrome)
Bring up IE and paste into the address bar:
You will get a popup saying something along the lines of:
Mozilla/4.0 (compatible; MSIE8.0; Windows NT 5.1; Trident/4.0;
Followed by a number of ".NET CLR" versions. If 2.0 is in there (and it is quite probable) then the installer just didn't need to do anything!