I got the error after some weird updates of windows media player.
The error messages looks like -
"The file wmp.dll has a version number of 11.0.0.**** where 11.0.0.**** was expected. Windows Media Player is not installed properly and must be reinstalled."
Solution for it:
1. Start -> Run
2. Type or Paste this -> c:\windows\inf\unregmp2.exe /UpdateWMP
3. Press -> Ok
Now try to open WMP.