I have the same problem as niaimani but I'm unable to add to his message so I'm starting this new thread.
This problem occurred after I downloaded IE 6 on an update recently. Then immediately after installing IE6, I discovered that my computer would not totally shut down when requested. (It took quite a bit of checking many things to discover that it was IE6 causing the problem.) I then uninstalled IE6 and the shut down problem disappeared.
However, since then I cannot use Outlook (this is a secondary mail browser so I only use it occasionally). I have attempted to uninstall Outlook 2000 (it is part of the Office 200 Pro suite) and re-install.
At 1st the problem did not prevent me from getting into Outlook but in my efforts to fix the problem I installed the Office SR1 update and since then, I'm unable to get Outlook to stay open since it gives the error message upon entry, and once clicking the ok, Outlook closes.
I just checked my Outlook Express (which I only use as a mail reader.) and it seems to be working fine.