Windows Defender Error MSASCui.exe Unable To Locate Component

If your Windows Defender gives you MSASCui.exe Unable To Locate Component error on your Windows, one would on a Windows XP machine normally try to uninstall Windows Defender and then try to install it again. But you cant do that in Windows Vista and later, as Defender is integrated into the OS.

MSASCui.exe – Unable To Locate Component.

This application has failed to start because MpRtMon.DLL was not found. Re-installing the application may fix this problem.

Windows Defender

MSASCui.exe is the Defender’s User Interface application situated in C:\Program Files\Windows Defender folder. MpRtMon.dll is Defender’s ‘Realtime Monitor’ dll, situated in C:\Program files\Windows Defenderfolder.

There is also no way you can really uninstall Windows Defender without facing other issues. Moreover, if you try to install Defender over your earlier installation, you will probably get a message that you don’t need to install the program because it already comes with Windows Vista. There will also be no option to continue the installation. The installation would just stop!

Nevertheless, you can try this trick if your Windows Defender throws up this error on your Windows every now and then.

First Run System File Checker. To do this first type cmd in the Search Bar but DONT hit enter. Rt-Click on cmd and choose Run as Administrator.

The copy-paste the following command sfc /scannow and hit enter. All your system files will be scanned by the System File Checker and if all your files are in order, you will see a message “Windows Resource Protection did not find any Integrity violations“. However, if something is amiss, it will attempt to replace the corrupt system files.

See this post, if you receive Windows Resource Protection found corrupt files but was unable to fix some of them error message.

As mentioned earlier:

  • MSASCui.exe is the Defender’s User Interface application situated in C:\Program Files\Windows Defender folder.
  • MpRtMon.dll is Defender’s ‘Realtime Monitor’ dll, situated in C:\Program files\Windows Defenderfolder.

However its copies can also be found in the following folder/s :




You will have to ‘unhide hidden files’ and ‘show system files’ from the Folder Options, to be able to see them.

The last numerals may differ, but essentially these are the folders. The winsxs folder is the native assembly cache. Libraries which are shared by multiple programs are stored there. You may also find different versions of the same dll files in these folders. Login as Administrator and try to replace the dll in the /Windows Defender/ folder with one of these dll‘s. Reboot and see if it helps.

Hope this help!

This post was written for WinVistaclub. It has been updated and ported here.

Windows Defender is turned off or not working may also interest you.

Posted by on , in Category Security with Tags
Anand Khanse is the Admin of, a 10-year Microsoft MVP Awardee in Windows (2006-16) & a Windows Insider MVP. Please read the entire post & the comments first, create a System Restore Point before making any changes to your system & be careful about any 3rd-party offers while installing freeware.


  1. Great article! Thanks for explaining what the MSASCui.exe file is and how serious it is to a computer system. I remember sometime ago when I had a MSASCui.exe error. I was literally going nuts! I had trouble finding information and when I did find information, the tech language was just too much for me to handle. Finally after weeks of searching, I stumbled on this article [] which provided some really good info on the file. I also watched a video [] which actually put things into perspective. I hope computer users who are struggling with the MSASCui.exe find your post because its really good.

  2. shawn housby

    Windows Resource Protection could not perform the requested operation. help me fix this asap

  3. Tom

    Thanks Anand! I had searched for days trying to resolve this problem and your sfc /scannow suggestion did the trick.

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