Its a very common problem and occurs when you install a new Windows Media Player skin by replacing "wmploc.dll" file in "System32" folder.
Actually almost all WMP interface resources are stored in "wmploc.dll" file and most of the designers modify this file and replace existing resources with their customized ones to change the UI.
But "wmploc.dll" is a system file and whenever you start Windows Media Player, it checks the version number of this file and if a different version number is found, it shows an error message "Windows Media Player is not installed properly and must be reinstalled" similar to following screenshot:
As you can see in above screenshot, the error message indicates that the version number of "wmploc.dll" file should be "11.0.6002.16489" but the current file's version number is "11.0.6001.7000". It happened because the new file version number was different than the original file.
To fix this problem, you can restore the original "wmploc.dll" file but if you want to use the new customized file, then you'll need to follow a few simple steps which are as following:
METHOD 1: Using Command Prompt
1. Click on "Start button -> All Programs -> Accessories". Right-click on "Command Prompt" and select "Run As Administrator". If you are prompted to enter password, enter the password and continue. You can also open Command Prompt in Administrator mode by typing "cmd" in Start Menu Search box and press "Ctrl+Shift+Enter".
2. Now provide following commands one by one:
3. It'll sync the WMP version number with Windows Registry and your problem should be solved.
METHOD 2: Using Resource Hacker
If the above method doesn't work, you can try following method which requires a little expertise.
Version Info -> 1
2. In right-side pane, you'll see the file version info:
You'll need to replace all instances of the version number with the required and correct version number. For example, the new customized file contains version number "11.0.6001.7000" but the correct version number should be "11.0.6002.16489". So you'll need to replace all instances of "6001" with "6002" and all instances of "7000" with "16489" as shown in following screenshot:
3. Once you correct the version number, click on "Compile Script" button.
4. Now save the file at some other location, for example in D: drive.
5. Rename original "wmploc.dll" file present in "System32" folder to "wmploc_backup.dll".
6. Now copy your new modified "wmploc.dll" file to "System32" folder.
7. Restart your system and after restart Windows will start using your new modified file and you'll be able to start Windows Media Player without any problem.
PS: If you don't have much idea about Resource Hacker, please go through following tutorial: