Shares Dissapear with W2K Server SP4

I upgraded from W2K Server SP3 to SP4 on a fileserver that has a few shares which many people in the company constantly access. About 2 times a day now, the fileserver loses it’s shares and no one can connect to their mapped drives. There is no longer a sharing option when going into properties of a folder. When I reboot the machine, the shares are back and working perfectly until the next time.