Well, look here:
The Internet connection has timed out.
I know you aren't using the software this refers to, but 0x800C000B is just a wrapper around 0x000B which is the underlying error.
I'm sure you are aware that the last 4 hex digits in an error code designate the underlying fault (e.g., 0x0005 is a memory fault, unable to read and/or write to a given address). So it would make sense that if 0x000B indicates a timeout that indeed my guess that you have a connection error--likely a timeout--is the underlying cause.
I would bet that 0x000B is mentioned in some C++ ".h" header file in the MSDN Library, but I couldn't find it in what I happen to have on this machine. I've got a lot of the old Library CDs, but it would take a loooonnng while to rummage through all of them.
So the problem may not be on your end. It might be that the receiver of the POST data isn't capable of processing the data fast enough. But this is still just a (slightly) educated guess.