Manually install the two voxatc windows (if you want both the past coms and the VOXATC window). Find a plane that has the voxatc windows successfully installed and copy those two window entries into your plane's panel file. Make sure you adjust the window ID numbers to match the next consecutive number available for the plane you're installing it to - it rarely matches the one you're copying from. It's all in plain text in the Panel file of each aircraft so it shouldn't be difficult to replicate in your new plane. Just to be safe - back up the panel file before changing it.
John