Hi,
I'm a newbiie but found this whilst i had problems with Media player 11. Here is how i fixed it. After uninstalling, reinstalling and finding you can never fully remove your library by running uninstalls i realised it must be something in my profile which was causing the problem.
N.B. THESE ACTIONS WILL COMPLETELY REMOVE YOUR LIBRARY MEANING YOU WILL HAVE TO REBUILD IT FROM SCRATCH.
In this example i will be using the C:\ drive as my home drive where Windows is installed.
Make sure you have set hidden files and system files to show.
You will first have to stop all the media sharing processes, to do this hit
CTRL, ALT & DELETE click the processes tab and order them by name by clicking Image Name. Scroll down to 'W' and stop all the processes begining with wmp. There are 3 or 4 I think. It will pop up a warning after each time you attempt to stop a process just click yes.
Navigate to C:\Documents and Settings\
user_name\Local Settings\Application Data\Microsoft\Media Player in explorer.
Rename the file Currentdatabase_***.wmdb. to Currentdatabase_***.bak (*** being the library version mine was 360.)
I also deleted all the other files in here.
Once you restart Media player your library will be blank. You will need to remove all the directories in the library that you are sharing or else the offending video file will once again be in your library and you will be at sqaure one. Luckily I knew that the offender was an AVI file and I removed the particular directory from my library. Codecs are a nightmare in WMP 11.. I now convert all avi's to WMV using VLC. Go
Here To get instructions of how to convert using VLC.. I did this to get streaming working on my Xbox 360.
The conversion takes about 20 minutes for a 110 minute movie.
Hope this helps.