[Fix] Microsoft security essentials version2 install & upgrade fails, Error code: 0x75633fbf

Trying to upgrade or install Microsoft security essentials Version 2 an it fails with the following error

The instruction at 0x75ef3fbf referenced memory at 0x00xxxxx. The Memory could not be read

And the error dialogs looks similar to ones given below? Then Read on on how to fix this:

[caption id="attachment549" align="aligncenter" width="570" caption="Error While Upgrading to Version 2"][Microsoft Security Essentials Version 2 Upgrade Error dialog ](http://www.gaurishsharma.com/wp-content/uploads/2011/02/mse-v2upgradeerrormemorycouldnotberead.png)[/caption]

[caption id="attachment550" align="aligncenter" width="300" caption="Same error, when trying to install a fresh copy MSE v2"][Microsoft Security Essentials version 2 installation error dialog ](http://www.gaurishsharma.com/wp-content/uploads/2011/02/mse-v2errormemorycouldnotbe_read.png)[/caption]

The Problem Explained

This issue may have been caused as some of Microsoft Security Essentials (Version 1) files would have got corrupted during the upgrade process on your computer or some for worse, some important system files need by windows have have been effected. In my case,  <!-- more -->I received an error message while trying to upgrade Microsoft Security Essentials to the latest version on my Windows 7 Ultimate based computer. you will also get the same error if you first uninstall Microsoft Security Essentials (Version 1) from Add/Remove Programs and try to install Microsoft Security Essentials (Version 2). This was weird error message that I have not seen before. Clueless on what this particular error message meant, I searched via google using the error code 0x75ef3fbf as keyword. found nothing, then search a bit more using "Microsoft Security Essentials Upgrade Errror". found hundreds of people were facing difficulty in upgrading to version 2 but its my back luck, the error I got(0x75ef3fbf) is unique error & nobody else apart from myself got that error. so contacted Microsoft Techical Support team by submitting a support case and they helped me fix this error. I am happy to report that after trying to this issue from past 15days, this issue is SOLVED!

Step-by-Step Guide on how to fix

Step 1 :- Uninstall the traces of Microsoft Security Essentials which was partially installed during the upgrade.

Step 2 :- Run Scan to verify integrity of all system files

Step 3 :- Reinstall Microsoft Security Essentials.

Note: Please try the following steps in the same order as provided above. If Step 1 did not work, please proceed to the next step. Please note down any error messages or notable changes you find as you try the steps. Post them in comments, I will try to help you

Troubleshooting Steps

Step 1:

Step 2:

FOR XP: Click Start -> RUN -> type CMD in the Run Window and then hit enter.

FOR Vista and W7: Click Start -> All Programs -> Accessories -> Right click on Command Prompt and select "Run as Administrator".

Step 3

There is a strong chance that important system files might have been corrupted. so its best to run System File Check(sfc). here how to do this

Scan will take few minutes to complete and after a while. If there were some files corrupt, you will get this kind of message:

[caption id="attachment551" align="aligncenter" width="300" caption="Example SFC screen shows that there are corrupt system files"][Example SFC screen shows that there are corrupt system files](http://www.gaurishsharma.com/wp-content/uploads/2011/02/sfcerror.jpg)[/caption]

Step 4

Now, we have removed all traced of MSE v1 and also repaired system files using sfc scannow command. lets try and install MSE v2

If you followed everything correctly, then this time MSE verion 2 should install normally without any error. it took me and entire Microsoft support team 15days to find a solution but I am posting it here, so you guys don't have to suffer.

Happy Fun and keep using this excellent Free Antivirus from Microsoft!