IIS7 rejecting POST requests with 400 error

I have a web application that is supposed to handle post requests from SAP.

This has been working fine at other customers with win2k3 systems (IIS6) and win2k8 (IIS7) systems.

However, on this specific customer's site, IIS responds with a 400 response, without calling my aspx page. In fact, I don't even see it appear in the w3c log for the virtual directory.

I do see the request using Network Monitor, so I know no firewalls and the like are eating the request, and as far as I can tell, all of the fields of the request are valid (there is "content-length", it looks correct (this is a sending of a 28K tiff file - which isn't MIME encoded, curiously enough now that I think of it...)

Ideas?

You could check the HTTPERR log on that server. Maybe this blog post contains a hint how to solve the problem:

ASMX POST request fails with HTTP 400 erro when content-length size increases

First stop was to look at HTTPERR log on IIS box, Invalid verb error was report in it:

2009-03-09 21:30:53 10.1.48.56 42676 10.1.48.53 80 HTTP/0.0 Invalid - 400 - Verb - 

We found the answer, and it isn't wonderfully useful for non-SAP users.

The program making the request was a utility used by the SAP Front-End client called saphttp.exe. Turns out, the version the customer had was one that SAP reported having EXACTLY this issue - badly formed POST requests. I copied my version of the utility to the customer site and it worked.

Mark it up to SAP wackiness.