Geez, that's a heck of a response to some humor after an hour and a half.
If you are having light issues in a single corner, it very well could be any number of things. My guess would be that it is a light tunnel issue as this sounds similar to some other light tunnel issues I have heard of in the past. It's not easy to get to.
Have you tried pulling the projector down, zooming in/out and seeing if the issue persists? Have you tried different sources to ensure it isn't a source related issue? Bypassing the A/V receiver as well? You are sure it is a projection issue and not a screen issue?
Do you have any photos of the effect you could link to that can provide additional details of what is going on?