I hope you've found an appropriate answer as this is from a while back, but I'll still post what I have found so some other searching soul someday may stumble across this. I've suffered from this same problem as well. The result looks similar to the following http://ow.ly/E1xV There is supposed to be a bar about 25px high all the way across at something like 70% transparency. It's a single pixel opaque png image.
I also have searched on this a lot to which I have found nothing. I even tried to use the ie png error fixing script (which actually made the problem worse). Now I am not fully sure what is going on behind the scenes that causes the error...my wildest guess would be something to do with IE rounding the pixel someway or another because of the opacity? The simplest fix (and only one) that I have found is just make sure the png image is larger than 1x1. I've been going with 5x5 just to be on the uber-safe side.
