Not able to reproduce this constantly - screen shot is here:
http://i554.photobucket.com/albums/jj417/alchemist_bucket1/Screenshot2010-09-10at150113.png

You click the tower - click 's' - a green bar shoots to the left - the orange 'selling' spills to the left behind the game and beyond - the game continues fine but you cannot do anything with that tower.

Hmm, I assume this was a custom map you made? Did you do anything different with the sell times? (ie. make sell time 0)

A sell time of zero is a known bug and I have already fixed it in the next release.

Let me know if that was not the issue.

Thanks for taking the time to report it :)

Ah ok - that will be it.

Sweet :)