I know that this is 1 1/2 years old now but I will post an answer anyway in the hopes that it will help you and maybe others.
To get rid of this bothersome message, do the following:
Click start>Run>type the word regEDIT>click OK>My Computer>Hkey_Current_User>Identities>Software>Microsoft>Outlook Express>5.0>Click Compact Check Count. Change Value Data to Zero for both Hexadecimal and decimal.
That is it. That will fix your problem. You have to go back in occasionally to re-zero those values because the counter keeps incrementing up 1 each time you open Outlook Express. This problem plagued me too for a long time.