I was having a similar error installing php 5.3.3 with the Error Code 0x80070020 with a direction to a few lines in web.config in my www root directory (not the standard root directory).
The solution, while crude, worked perfectly. I simply deleted the web.config file and now everything works. I spent HOURS trying other solutions to no avail.
If anyone thinks this was stupid, please let me know. If anyone else has spent the same amount of time pulling out hair, try it and see (after backing up the file of course)
Regards FEQ