i have this same issue...it will not allow any new data from my oulook contacts or calendar to send to my n900, though i can add data to contacts and calendar on my n900, and it will sync to my outlook.

i believe it does have something to do with a calenar issue. it started in August 2011, after i had a bogus calendar issue happen.

i copy/pasted an item in my calendar, and somehow, it corrupted and made this entry for the year 4051! i couldnt get rid of it...

so i replaced my pst with an older one, and then that item went away, but i still cannot sync.

someone please help!