After reading many posts about people having this problem, I decided to try a crack at this to see if I could fix it.
1) I enabled root access on my Mac (OSx Lion)
http://support.apple.com/kb/ht1528
2) I logged off of my Admin account, logged in with root (click Other when login window appears and type root and the password you assigned). I got the memory is installed in the correct slots message, as usual.
3) I logged out of Root and logged back in with my usual admin ID. The message did NOT appear.
4) I shut down the system (powered it off), powered it back on, logged into my normal admin account (the one that was always getting the message), and like magic - No more memory message.
5) I went back in and disabled root (the opposite of enabling it in step #1) after the restart.
I did NOT have to fix permissions or reset anything. But, it seems that there must be some sort of permission thing going on if log gin in with Root fixed the problem.
I hope this helps others - this can be very irritating.