Thinkpad Advanced Mini Dock (250410U) Display Won't Extend

[corbin31]

I have a T400 (2764 CTO with a Radeon HD 3400), an Acer 23" monitor, and an Advanced Mini Dock (Part 250410U, Model 2504). I am trying to extend the display from the T400 to the Acer monitor through a VGA cable. When I plug the monitor directly into the laptop, the display extends. However, when I dock the T400 and connect the monitor to the Mini Dock, I can't get a signal to the monitor. Any thoughts? Thank you.