Screen removal problem

[bogen2]

I tried posting this at the “other site” but had no responses so thought I would try here. I am trying to remove the screens in the small vertical-sliding windows in my rig to clean them. The window only partially opens and I can’t see how to get the screen out. It slides up and down in its channel but doesn’t seem to want to come out. The screens pop out easily on all the other style windows.

Anyone figured this out?

Bob