Laptops Losing Connection On My Office Network?

I have 2 older xp pro tough books that connect to my domain via a pair of versa vx 400 access points. automobile technicians use these computers to communicate with cars via a separate wireless card and WiFi device (SPX MVXI) that broadcasts a wireless signal.they always connect just fine to the network but sometimes they drop there connection and don't rejoin which screws up my scheduled tasks (nightly upload). They will reacquire the connection every time if i select it again manually in the windows wireless config.here is what I have done so far

1. set up exclusion range in DHCP distribution on my DC

2. set the laptops up with static IP's within the exclusion range.

3. configured the laptops to auto connect to the network even when its not broadcasting

4. set the access points on channel 7, and the devices on 1 and 11.

I have done a lot of research on this issue, a rep from versa told me that Intel proset wireless isn't very compatible with there product which i this is BS since it does the same with with the netgear WiFi PC cards.