Your question on Microsoft Answers has received a reply:
Question MSE says I have not scanned recently when I scanned that very day.
Reply
Hi Byzantine,
Please see the following compliments of Le Boule:
Are you using CCleaner? Piriform has programmed it for some reason to remove part of the MSE History files and it's deleting the files MSE checks to determine the last time a scan was conducted. This file removal has no effect on the antimalware protection provided by MSE.
Open CCleaner Applications Tab, then Under Windows uncheck MS Antimalware...that should prevent CCleaner from deleting the MS Antimalware scanning history files.
Per suggestion of MartinHampton you may also need to uncheck MS Management Console.
You may need to run another quick scan and reboot the computer.
See this thread for more details and alternatives to resolve this problem if you are not using CCleaner:http://answers.microsoft.com/en-us/protect/forum/protect_start/why-after-a-couple-of-days-after-a-scan-does-my/0dc5b433-28ec-4180-a8ee-26a6cd10c3ab
If that isn't it, please check your system clock to make sure it is correct (even a few minutes can matter - but I've seen it say 1978 or 2286 for the year). Resync it with the internet clock. If it need to be changed and keeps happening, change the CMOS battery on the motherboard as that's almost always the cause of a system clock problem.
Please see the following compliments of Stephen Boots – MVP:
What operating system and service pack?
Prior Security Software?
Any security software still installed?
A possible reason for this problem is that you have conflicting security software installed fully or partially on the PC. Remove all other security software from the PC. Reboot.
You may need to use a cleanup tool to remove your prior security software:http://social.answers.microsoft.com/Forums/en-US/msestart/thread/407bf6da-c05d-4546-8788-0aa4c25a1f91
Be sure to review this post: Check list for installing Microsoft Security Essentials (also found here: http://experts.windows.com/w/experts_wiki/89.aspx)
If that fails to resolve the problem, open an email support case:
{SNIP}
I hope this helps.
Good luck!
{Snip}
