Looks like a common problem with Outlook, AS or Exchange. I found a link:
http://pdaphonehome.com/forums/showthread.php?t=58216
There's a microsoft link with fixes but it involves having access to the Exchange server(I don't know if that's what you sync to though).
Some have fix the problem within Outlook or AS. Give it a try with Post #'s #18 & #19.
Good Luck.
edit
I found some other links here on our forums you might want to check out:
http://www.aximsite.com/boards/showt...ght=0x85010014
http://www.aximsite.com/boards/showt...ght=0x85010014
There are three others that came up, one of which was this post, another with Small Business and the last with Groupwise.