This page shows the kind of window I have and how to remove it.
Problem: one side of the window is stuck and won't come out. The window in question is labeled "left-hand sash" in the illustration and the right side of the window is stuck.
How it works: There are 2 metal pins on the top of the window and two on the bottom (one pin per corner). The pins slide in a groove at the top and bottom. To remove the window, you lift it up so the pins can clear the groove in the bottom sill, which is made of plastic and not removeable without removing the windows.
It appears that the problem is that the space between the top of the window and the casement above it is too small on the right side. Thus I can't lift the window up high enough for the pin to come out of the track in the sill. It's off by about 1/8", I'm guessing. In other words, the window isn't square with the casement. The cause may be swelling of the wood due to humidity, or settling of the house; I don't know.
It's urgent that I remove this window because there's mold in between the double panes and the panes need to be replaced. Any ideas how I can get the stuck corner out? Thank you!