One day without any changes to settings I turned on my Pioneer VSX-56TXi Receiver and it would not respond to it's own (original) remote control. The Remote Control works as before with other components of my Home Theater. I did look in to resetting the Pioneer but it didn't help.
Any sugestions?

I've never heard of the IR circuitry going out of a piece of electronics, but my first impression is this is what may have happened here.

Batteries?

But, it works with his other pieces of equipment. But yeah, batteries would have been the first thing I would have tried.

Might seem like a "silly" question but I am assuming that the front panel buttons on the AVR are still functioning as normal? Has there been a recent firmware update to the unit?
Mainstream manufacturers, like Pioneer, will have multiple IR codes for various equipment and I wonder as well, somehow, has this mysteriously changed especially since you stated all other components commands remain intact? Another possible option is in many cases there are a number of ways of re-setting the remote, however, in doing so, it may result in a loss of commands for your other equipment and would require a re-install. What does the manual say about this, if anything?

Other than that, I guess a call to Pioneer is in order. The problem is, like most mainstream manufacturers, trying to get a helpful and timely response from these people can be like "pulling teeth".