GX260 losing network connectivity

We are running approximately 100 GX260's on a domain. They keep losing their network connectivity randomly. The computers are running Windows XP and a program called Deep Freeze (for security purposes because the computers are in a school campus enviromment) that allows no changes to the system when it is "Frozen" or locked. We run this program throughout many of our buildings on various lab computers and do not have this issue with any other model Dell incluing GX270, GX1 and GX110. The machines are setup and "frozen" with the domain connection on. They will be fine one day and then suddenly have no connection the next day after being powered down.The problem seems to coincide with one maching when it had message having to do with a low CMOS battery power upon POST. A day or two after this it then dropped the network connection. The pc is still joined to the domain it just will give the error message that the domain is not available when you try to log on to the network.  Sometimes they get the battery error but most of the time they do not. The machines are still setup exactly the same and no software changes have been made. The machine has not disjoined itself from the domain it just cannot get to the network even though the physical connection is recieving data (it is light up and working). Rejoining the machine to the domain solves this issues but then it will sometimes happen again. So far, we have resorted to replacing the CMOS battery and the machines in which we have replaced the battery seem to be doing ok without dropping their connection. (This may be a coincidence.) It seems like something is happening with the battery losing power and the network connection (physical) when the machine is shut down. Is this a problem with this particular model. It almost seems like a CMOS problem with the motherboard losing some sort of communication with the network port itself? Frankly everyone here is throughly confused and are wondering if this is some sort of GX260 problem similiar to the bad motherboard problem we have encountered with the GX270's.