We have just replaced a Customer's domain controller with a new 2008 R2 server running Active Directory in Native mode. Most of the project went as expected but there is one trouble PC (Windows XP SP3) that keeps losing connection to the server. It only connects to a shared folder to open, use, and then save files. Seemingly randomly the machine will decide to lose connection to the server and not allow any traffic to the server - PING, DNS queries, DHCP requests, anything - but you can browse and ping to other addresses in the network totally normally.
The XP Machine is wireless to a nearby access point, and is one of very few wireless PCs. I've adjusted wireless settings and upgraded firmware on the Dlink but I don't think it's actually a wireless issue (See the above about pinging and browsing other addresses).
When this happens there are no errors created in Event Viewer under System or Application, and no indication that anything is wrong. It's free of malware and doesn't have internet access (has a bad gateway set). Everything I've read says there isn't any reason an XP SP3 machine would have problems with a 2008 R2 domain.
Please let me know if there is any other info I can provide, and thank you in advance