On Fri, 04 Sep 2009 08:32:13 GMT, Chris J Dixon
wrote:

If you try to pass the drill back through the hole, does it still
go? Can you pass a stiff but flexible wire through the hole?

It is possible that a fragment of the concrete that was disturbed
during the drilling has now dropped and is obstructing the hole.

You can pass the drill through the hole, in fact you can see through
the hole, so the hole is clear, it's just that it slopes an inch/two
inches downward!