cant update MSE definitions using windows update.

The KB2310138 is the actual MSE update. The part you need to look at is the actual Definition number which is the part in brackets.

I had trouble with one going back to the end of August & early Sept., which was KB2310138 (Definition 1.249.211.0). It would install every time & the update that came with it would fail. I eventually solved it by hiding definition 1.249.211.0 before it installed again & since then all has been working perfectly.

Hi,
You could remove and reinstall mse
http://support.microsoft.com/en-us/kb/2483120

When I used mse this was a better way to update these types of updates posted by davidE a while back :)
How To Fix Microsoft Security Essentials Virus Definitions Updates

Hi,
If no joy there are better alternatives that update flawlessly :)
I personally use panda free it is as lightweight as it gets but there is also bloated avast that seems to be popular.

macgig said:

this one looks like it installs then shows up again in windows update after a few minutes. no idea how to fix it and get it to install.

That's what was happening to me. Make a note of the offending MSE update, particularly the Definition number, & after a while open Windows Update & click on Check for Updates on the LH menu column. Wait until updates come through & then click on the new ones showing, so you can see what they are. If the offending MSE update is there, Right Click on it & select Hide. That will prevent it downloading again.

The above fixed mine & MSE updates are now working perfectly.