This is what I was thinking as a last-resort option...
I would suggest trying to add some of your solder as you do it - sometimes this helps it melt the old stuff.
Could you borrow a hot air gun? hot plate?
What power is your iron?
OK, I can try that.
I was considering just buying one from harbor freight for SMT soldering, but if my iron can't even do it...
The transparent glaze could be "conformal coating". It's not cheap, but you can get conformal coating remover:http://www.newark.com/techspray/2510-p/conformal-coating-remover-1pint/dp/69K7673
You may want to play around with household solvents too in case you're adventurous: good old isopropyl alcohol, nail polish remover, etc.
If you have a bigger tip for your iron, try switching to that. Often it's not the temperature that fails to melt/solder joints it's the lack of thermal mass to transfer heat to the joint (i.e., tip size).
Jeez, that is expensive... I tried acetone, and I don't think it did anything. I'll try using the bigger tip, but my precision tip has never been insufficient for simple thru-hole stuff before...
It might be (without seeing pics of what you are working on, of course) because it came from a UPS or similar, that it has high-current traces or such with a lot of copper, and if there is enough solder - simply acting as a large heatsink; the heat gets drawn away quicker than it can melt the mass of solder. The conformal coating is likely not making things easier.
I would go for the heat-gun and/or hotplate (or maybe toaster oven) approach - whatever you do, though, only use an oven or hotplate that won't -ever- be used for food again (lead and food don't mix - well, they do if you want lead poisoning). You need something that can deliver a lot of heat over a large area; much more than a pinpoint of 40 watts.
You will want to do this heating outdoors in a well ventilated area - a fan to blow any fumes away from you would be helpful. I wouldn't worry about the conformal coating in this process, as it will likely melt/burn/vaporize under the heat (but if you want to try to remove it, you can try a variety of solvents; you may have to soak the board overnight - let it dry completely before heating). You will also want to wear goggles, perhaps a face shield, gloves, long sleeves, long pants, and shoes. Why will become apparent shortly.
The simplest thing to do would be to mount the board parts side down between a couple of metal bars or such (something high-temp heat proof), then put a box or a pan or something underneath the parts side (to catch the parts), then use the heatgun (or heat the board up in the hotplate or oven) until the solder is melted, then use a board, or a rubber mallet to tap the board/parts to force them out and into the pan. You'll want to secure the board well so it doesn't bounce and fall, but so that it it still "springy" (maybe use some c-clamps at the corners) when struck. Because the solder will be molten, it will probably splatter around, hence all the safety gear I suggested wearing.