Your husband's computer was setup for use on his company's domain network. His user name and password is associated with his company's domain.
When you setup the laptop for YOUR company's workgroup, you effectively took it off of HIS company's domain. Now, it doesn't know what to do.
In order to fix it, have your husband take the laptop back to his office, and tell the I.T. guys to put it back on the domain. Then he will be able to log in again.
Here is a tip: if it's a work computer, don't screw with it. I don't mean to be rude, but companies often have their computers set up a certain way, and tinkering with these things often break them. Check with both your company's I.T. dept as well as your husband's to see what you can and cannot do without causing problems.
Hope this helps.