I just installed a new KitchenAid dishwasher in my tenants apartment. 
They said that they are having a hard time opening the door to the
dishwasher.   I don't have time to go over there at the present time,
so I was wondering if anyone might be able to provide some insight as
to what the problem might be.

Could it be due to the plumbers installing it incorrectly?   Or is
there a special way for it to be opened after running through a wash
cycle?   Or is it something else altogether?

Some dishwashers have a safety interlock switch to prevent the door
from opening when water is in the machine. It's possible that the
interlock switch is malfunctioning.

You might find some helpful information here:

http://www.repairclinic.com/0088_9_1.asp#Level1_8

There are some links in this answer to an earlier GA question that may
be useful:

http://www.answers.google.com/answers/threadview?id=136114