On Tue, 31 Jul 2012 12:40:14 -0400, willshak wrote:

Note: I tried four times to drill deeper holes but there is a solid
steel plate in that wall (apparently) that nothing can possibly dent.
What is it, I don't know! ???

You probably hit a metal framing hanger (or framing metal hanger) in
that first area.

Whatever it is, it's big because the two bracket holes are a good four
inches apart, and I drilled four of them, about six or seven inches
apart, so the impenetrable object is (at a minimum) four inches by six
inches large.