I had the exact same problem. Here is how I fixed it:

close outlook
Goto control panel
add/remove programs
remove outlookaddinsetup
Restart

Everything should work just fine now.

"Fred R." wrote:

I have a user that when she schedules something in your calendar, she
receives a recurrance for the same entry even if she didn't schedule it to be
a recurring event. Even after hitting the remove recurrance button, the same
appt. is showing on the same day, every week. Any way to prevent this from
happening or any idea as to why this is happening. I was able to schedule
something in my calendar with no problem..Thanks in advance