Windows Mobile Not Syncing Over Wireless

We have a number of Titan HTC-PPC6800 PDA's. When we sync through the PC USB/Active sync everything syncs fine. When we try to sync over the wireless we always get an error 0X80072EFD meaning the network is currently busy try again later. If we restart our exchange server it will work for an hour then not connect again. I have seen numerous post's but no answers on this problem. Any help appreciated,Thanks.