I had this same problem on a Win2K Professional machine with Outlook
2000 SR1. I was only getting it on one user so I deleted that user's
folder in C:\Documents and Settings\ and then recreated just by logging
on as him again. Of course, before I deleted his folder, I copied
anything useful out of it like his Favorites folder, his My Documents
folder, his .pst files in C:\Documents and Setting\user\Local
Settings\App Data\Microsoft\Outlook\ You might actually want to just
copy the entire user folder in case there is anything in there that you
don't know about.
This problem did appear to be related to the MAPISP32.dll file but I
could not find a solution except the one described above.