Win98 changing doamins while up?

I have an issue that is bugging me.

I user claims that their domain is changeing while they
are logged in. THe domain is supposed to be 'X' and then
it goes to 'Y' blocking them out of the services
from 'X'...

Is that possible? I thought that the domain would stick
once set in the Microsoft network client int he control
panel.

Now it appears that it moves to another domain.

They logout and back on when they get the denial message
and then can't find a domain server because there is
no 'Y' domain...

The names have been changed to protect the innocent...

What is going on. I keep blaming the user. Is it the
user???

Thanks for any enlightenment...