Periodically the Kaspersky Outlook plugin stars to misbehave, causing a pop-up warning every time a user tries to send an e-mail message. I found a straight forward solution at the following site: http://www.fixkb.com/2010/03/add-in-kaspersky-mail-checker-cannot-be.html

I had to change the suggestion slightly to reflect the Windows 7 path difference from XP.
There is also a typo on his page (there are too many “l”s in his CLI example for .dll).
Also pay attention to the version number in the path.

regsvr32 -u “C:\ Program Files (x86)\Kaspersky Lab\Kaspersky Anti-Virus 6.0\mcou.dll”
regsvr32 “C:\ Program Files (x86)\Kaspersky Lab\Kaspersky Anti-Virus 6.0\mcou.dll”