LAN connectivity problems

This may not involve hardware but it is a netoworking question so it may be better suited somewhere else.

I have a network here with over 2 dozen computers, at least 3 of which are servers. 2 are running Windows Server 2003 and one is running Windows NT Server 4.0. One of the 2003s and the NT are in a Workgroup with the rest of the computers the other 2003 is in a Domain. All the computers have fixed IP's except for the laptops. One of the laptops, running Windows 2000, has recently been having problems with connecting to mapped drives. When the laptop is turned on the mapped drives connect but usually within a half an hour they get red Xs on them, and when they are opened the following error is given:

"An Error Occurred while reconnecting S: to \\server\folder. Microsoft Windows Network: The Local Device name is already in use. This connect has been restored."

When the NT server is mapped and this happens the laptop ceases to recognize any of the computers in the workgroup and the domain. If one waits long enough it will be restored.

That secondary problem doesn’t occur with the 2003’s and they return much faster.

Also, it will not enter the domain itself but the Server inside of it can be accessed by typing it into the address bar, but that may be unrelated.

We have seen a similar problem very temporarily on 2 other computers but that may not be related and those problems were very minor.

If the laptop is restarted with the drives mapped, the process is restarted again.

However if the mapped drives are disconnected and then the computer is restarted the connectivity that would lost when the mapped drives stop working will stay up. It is lost periodically but it will usually come back, if you attempt to access it in a different way, which may be because it takes a certain amount of time to try it another way and the connection resorted itself by then.

However the internet connection through the LAN is never lost. When I first got to the computer it wanted me to set up an internet connection and gave that whenever you create a new user but if you get it not to do that anymore it connects just fine.

I am always able to ping the two workgroup servers but the domain server I could ping completely once but other times it has either always timed out or timed out the last 3 times. I don't know why regardless it seems that trying to ping anywhere, even if it doesn't exist,/sever/computer will always fix the problem immediately.

I have recently come to the conclusion that it’s loosing connection to all of the other computers for very short periods of time and when this happens with the NT Sever is causing a lag. Does anyone have any idea as to why such a disconnection is happening or how to keep the lag from happening?

I have tried installing a different Network card, which gave me the same problem, running NET USE * /delete, which told me there was nothing there to delete, replacing the hosts file, mapping them under different letters, moving the laptop to a different location, setting a fixed IP address, changing the default time-out period, and creating a different user name, which also gave me the same result. Does anyone else have any ideas?

It is also possible that restoring the connection takes at least some fiddling around with. But I don't know because the only way to check is to attempt to connect.