I was trying to join a game with a couple friends who have BG:EE for their Ipads. I could not join the game, I recieved an error saying that they had version 1.0.2009b and I had version 1.0.2011.
After searching everywhere for a way to download v 2009b, I decided to just edit the baldur.exe file and hack it so that it thought we had the same versions. Totally works. The game is still kind of buggy, we have crashed twice in 2 hours, but at least it works.
To change the version number, I downloaded a Hexidecimal editor, hexedit from here http://www.physics.ohio-state.edu/~prewett/hexedit/
Then I opened Baldur.exe from the games main directory, then did a search for my version number, "2011", and changed it to "2009b". It was found on Hex line 526090 on my computer. Right after a section saying "fake touch UI... Scrn...." attached is a screen.
Im pretty sure this should work with any version error you get. But maybe not. Use at your own risk, and probably make a copy of the .exe before editing it.