Edit: I didn't realize he had already done the following, and it didn't fix it for him. It did fix it for me however, so I'll leave it for anyone else that comes across this thread with this error.
I know this is an old thread, but it comes up pretty high in a Google search, so I figured I'd post the answer.
Apache2 will still try to use the file auth as the primary authentication source. If the AuthUserFile isn't set, you get the bad file descriptor error. If it is set, then Apache only uses that. The fix is to add this:
You may also need the following:
I don't think you do, but I haven't tested without it.