(vla-get-activepviewport) Stopped Working

[jackgnc]

I have a lisp file that always runs on all 20 of our AutoCad 2008 computers in the office, and last week one of the computers started returning the error message "QueryInterface IDispatch fails." I've traced the problem back to the (vla-get-activepviewport) function in my lisp file. I haven't changed the file in months, and I can't find any system variables that are different on the problem computer.

Anyone have a clue what might be causing this?

Jack