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 isĀ "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 Startmenu Search box and press "Ctrl+Shift+Enter".
2. Now provide following commands one by one:
unregmp2.exe /updatewmpversion
regsvr32 wmp.dll
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.
1. Open "%windir%\System32\wmploc.dll" file in Resource Hacker and go to:
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 and save the file.
That's it. Now 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:
All About Resource Hacker in a brief Tutorial
This article was posted by VG in following section: Resource Hacker, Troubleshooting, Windows 7, Windows Vista, Windows XP.
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Osku Kaskisola
nice 1
wilson
VG...Could you pls post the original wmploc.DLL 6002.16497 ??? i lost it...!! i 4got to make back up! pleas...
Nikolaj
3v4n the h@xxor
Thanks VG :) one question though. MY error message said that it wanted 16497 rather than 16489. What is with that? (don't worry, I fixed it :))
wilson
VG !! Thats so great of you..Thanks a lot 4 helping me...its working now.. :) ..Luv ur site... !! ;)
gary
I followed the steps and compiled the script, when it cam to save it said it could not save the file as "%windir%\System32\wmploc.dll", i asked for it to replace it but no success, what to do next??
Terry
I thought I did everything right.I changed all the lines from 7004 to 7000 and saved the file.
Then I hit the compile Script.It asked me If I want to save over the existing file, I said yes, but then it told me it couldnt save it. Help!
Says it cant save it
VG
Take ownership of the file using following tutorial:
http://www.askvg.com/add-take-ownership-option-in-file-folder-context-menu-in-windows-vista/
Or save the file at some other place and then use "Replacer" to replace the file.
Toobig
Took ownership, used replacer (which failed) set permission to full control, and it will still not copy.
Tried the whole process in safe mode as well and still no joy. This is really frustrating!!!
Any other suggestions?
VG
^^ After taking ownership, rename original file to some other name like "wmploc_original.dll" and then paste the modified file in "System32" folder. Restart your system.