MSE 0x80070645 Error

Today I had a call from my brother saying that he is having some problems updating his Microsoft Security Essentials on his W7 PC. After running through a few things with him and having a remote session we still weren’t any further, so I suggested that he drop it off so that I could take a `Hands On` look at it.

I was somewhat miffed that I couldn’t install a simple piece of software like Microsoft Security Essentials so made it my job to do so.

While I was waiting for the machine to arrive I have a quick look around on TechNet for the error code 0x80070645 and after sifting through a fair few results it looked like I had 3 options!

Reinstall the operating system – Seriously? Who does that these days?
Put in a support call to Microsoft – Again, seriously?
Install a different Antivirus – Yeah ok I get that, but that is not the point here.

Not willing to do any of those, mainly because I pride myself on trying to fix all computers that come my way without doing a reinstall or getting top level help. 99.49% Fix rate will tell you how serious I am about that.

I tried most things that were suggested by others that were in the same situation.

Microsoft Security Essentials Removal Tool (
That run and said that it had finished ok, but after a reboot MSE still failed to install with the same 0x80070645 error

Manual removal off all files, registry settings and services etc. using a script.
That run with errors as there were some files etc. that were missing because of the former uninstallation. Again after a reboot MSE refused to install with the 0x80070645 error.

I manually checked the file system, registry and services to see if there were any stragglers left over, but there were none.

I tried the install again and when the install failed again I checked the MSE installation log and found an error when it came to remove the mpfilter.sys driver which was odd as there was no mpfilter.sys driver on there?
I extracted all the files from the MSE installation and looked at the mpfilter.inf file to see what had been missed of the uninstallation, but could not see anything that was.
I copied the mpfilter files back to the computer and tried to install the driver again, finally having to recreate the service manually. I then tried to do the install again, and this time it got a bit further according to log, but it still failed with the same 0x80070645 error.

This was now a right pain as I had to copy the files over and recreate the service every time I wanted to run the MSE installer to trouble shoot the next thing that was wrong. More searching on TechNet and further afield did not give me anything else to go on.

I then tried one of my random thoughts – what happens if I install Forefront Endpoint Protection Client on the machine? I had looked at Forefront Endpoint Protection a while back as part of my TechNet subscription.

So I installed FEP, expecting it to fail given some of the similarities, but it installed with no problems, went off and updated and done a full scan. I saved the FEP install logs so that I could take a look and compare it to one of the failed MSE install logs that I had.
I then removed FEP and rebooted and thought I would try and install MSE again.
To my surprise MSE installed fine, updated and done a scan – no sign of the 0x80070645 error.

I saved the install logs so that I could compare the FEP install against the MSE install, but sadly my USB key stick with all my tools, utilities, scripts and install logs decided to die on me! Not a major problem as most of it is somewhere else, but the log files I could not get back.

So, I’m not sure why that happened or what the FEP install did that was different to the MSE install but it did fix the problem. I will have to wait for another machine to turn up with that error before I can take a proper look at the logs to work it out.

Thankfully, another awkward computer fixed.