Which version of AC and what platform are you on?
You should include these in your signature.
This may just be a GDL script error bug, you could open up the library part, command/control O and do a script check on the 3D window.
Or, as with other library parts, some of the windows might have minimum and/or maximum parameter sizes coded in and you are exceeding its limitation. Just a guess, but as you are working on a prison, perhaps you are trying to make your windows a narrow vertical slit and the narrowness might be the problem. Here in the states cell windows are something like 4-1/2" wide.
This said, could you elaborate?
A screen shot of your window settings would also be helpful.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"