Yes it is a strange error message. After removing McAfee Anti-Virus from one of my machines I kept getting this each time I launched Outlook:

I thought I could stop the error by going into advanced options and disable the old McAfee extensions. Unfortunately – nothing from McAfee was there

After doing some searching over at MS I found this KB article:

http://support.microsoft.com/kb/823633

The short version is:

Drill down to this registry key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Exchange\Client\Extensions

The delete the value named “Exchange Extensions”

Then launch Outlook again. Now the errors are gone, and Outlook will recreate the key.

I also realized that this bug was fixed in SP1 of Outlook 2003, so I promptly upgraded it so I would not have it happen again.

Lastly, it seems that the removal of McAfee was only coincidental – According to the MS fix these are the steps you can take to reproduce the error:

1. Send an e-mail message to a recipient by using the following method:
Right-click an object, point to Send To, and then click Mail Recipient.

2. Wait 24 hours or more.

3. Send a second e-mail message to a recipient by using the method that is described in step 1.

I had already upgraded to SP1, so I couldn’t try it out and see if this really was the problem, either way I am glad it was an easy fix.