"Class not registered" is one of the most annoying and frustrating error message I ever got because none of the video files can be played by Windows Media Player, Media Player Classic or other DirectShow player and common fix methods (Windows Media Player reinstallation/upgrade, codec reinstallation...) seems to fail.
Fortunately, the solution (in fact one of them because there are few different solutions) for this problem is very simple.

After some research I found that quartz.dll (a DirectX related DLL) wasn't registered correctly.


How to register it? Click on Start > Run... > and type regsvr32 quartz.dll
 

In the end, you should receive a message saying that your file was succesfully installed.
 

Note: Please, let us know if the solution suggested here wasn't helpful for you so we can try to complete this guide with other hints.

It didn't work for me. I downloaded some computer games and still can't open them.

Rating: 1 | on 13 Aug 2011, written by: evp

Has not worked for me,I get "windows can not find" is there anything else I can attempt ?

Rating: 1 | on 09 Aug 2011, written by: Freddy L McGuire

it didn't work at all for me, the file didn't successfully install.

Rating: 1 | on 27 Jul 2011, written by: KaTRINA

Amazing ! worked instantly ! searching for hours lol couldnt find nothing this took two seconds and worked to perfection !! thanks !!!

Rating: 5 | on 18 Jul 2011, written by: Chris

A miracle!! Wow! As others above I had frustratingly tried for weeks down many sidetracks!! It took a couple of goes but it worked. I think I wasn't leaving a space after the '...32'. For info and possibly help, maybe not related, my trouble began after I installed Nero 10 Multimedia Suite. It did not run - as with my other Multimedia players - except like 'WMV Maniac' above, for VLC . Again thanks a million. Now to try Windows Movie Maker which also had 'died' :-))

Rating: 5 | on 01 Jul 2011, written by: Laurie

You fixed it... I've spent 2 days downloading all kinds of software and codec.. and yet the fix is so simple. Thanks man!

Rating: 5 | on 23 Jun 2011, written by: Jeff

I tried and it worked. I am copying old cassette recording of grandmother and couldn't hear it. Now I can. Thanks.

Rating: 5 | on 23 Jun 2011, written by: Marilyn

It worked. thanks

Rating: 5 | on 27 May 2011, written by: user

NO. It does not work! My WMV still cannot play except for its played with VLC (VideoLAN).

Rating: 2 | on 12 May 2011, written by: WMV MANiAC

I cannot believe that the fix was so easy after I had spent a great deal of time going around in ever decreasing circles... Thank you so much for such an easy fix.

Rating: 5 | on 06 May 2011, written by: phil

I can't believe it was THAT simple! After hours of pissing about with codecs and dxdiag tests and who know's what. Brilliant thanks.

Rating: 5 | on 08 Apr 2011, written by: Steve

downloaded/installed directx, registered as directed above. still getting "class not registered".

Rating: 1 | on 23 Mar 2011, written by: scala

I got the successfully registered message but the error persists. It's the AVS DVD Player (a free version) that is now hard to find.

Rating: 3 | on 16 Mar 2011, written by: Jeff

Thank u so much. It worked..

Rating: 5 | on 04 Mar 2011, written by: Atif Ansari

Quartz dll failed to load. Something to do with binary. Tried to get info copied but would not paste here

Rating: 3 | on 26 Feb 2011, written by: Jack Anderson

How to install/uninstall DLL and AX codec files

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