NT Cached Login Problems

We have users that take their Windows 2000 laptops out of the office for weeks at a time.

They login to an NT 4.0 Domain when they are in the office. They logon using cached account information when out of the office.

After a while (using the cahced account) they get an error message that states
“Domain Controller could not be found for the specified Domain” and they can’t use their machine.

Is there any way to let them continue to use cached credentials?

Thanks for the help.