You said you set up a one way synch, Outlook to device only. I bet you need it to synch both ways. Whatever you do, don't mess with the OS/firmware. That's not the problem here. I'd call your provider and ask for a BB specialist if you can't figure this out. Somewhere I remember that the 8130 OS has bugs in it wrt calendar synching. You might try a search here as well.
BB 8900 Tmobile, Moto Droid Verizon