Network name no longer available

I realize this question may have been asked several times here , but I don't see it any where.
I setup my very small LAN , I mean tiny. Two computers on a crossover cable , no internet sharing.
In the past I have had no problems with any comps. , but on my new comp. , which is has Giga LAN, other comp. is 10/100. Reason I state this info is I feel like this may be where my problem lies.
Anywho, the comps see each other and I can begin a file transfer but after a minute or so it quits and gives me "network name no longer available" error.
I did some searching and found some info which said to adjust MTU by adding a few reg keys / values but it did not help.
Any input will be appreciated.



Edit: Do I need to use a CAT 6 cable instead of CAT 5? What is the difference? I am ignorant when it comes to networking.
Hmmm maybe I should research some more.

Well I haven't had the chance to dig into like I wish I could.
I did try disabling both firewalls , but to no avail , I also tried limiting speed to 100 full duplex also, nothing.
After some research, I see my CAT 6 question was a bit ignorant .
Anyway , I appreciate the input , and maybe soon I will get the chance to REALLY address the issue.
I didn't mention that the MB has dual LAN , no idea if that would effect anything . Don't see where it would.