New IIS 7.5 Installation On Windows 7 Generates Error 500 Without Logging Details When Posting ASMX Request

On my new(ish) Windows 7 x64 development laptop on which I've just installed IIS, I'm trying to run an .asmx web service compiled with .NET 4.0 and installed with an MSI from a setup project. But whenever I try to execute the service, either from SoapUI or from a .NET WCF client, I get an HTTP error 500 response. And I cannot find any further details about the error. This is what gets into the IIS log:

2012-05-17 21:51:23 10.10.14.155 POST /CwtReservationPushService/ReservationPushService.asmx - 443 - 10.10.14.155 Jakarta+Commons-HttpClient/3.1 500 0 0 121 
2012-05-17 22:03:45 ::1 POST /CwtReservationPushService/ReservationPushService.asmx - 443 - ::1 - 500 0 0 131

but nothing is logged in the system Event Viewer logs that I can find; and nothing is in the C:\Windows\System32\LogFiles\HTTPERR\httperr1.log file about an error 500. I installed the Failed Request Tracing and enabled it, but the only part that seems pertinent in the generated XML is:

ModuleName  ManagedPipelineHandler
Notification    16
HttpStatus  500
HttpReason  Internal Server Error
HttpSubStatus   0
ErrorCode   0
ConfigExceptionInfo     
Notification    MAP_REQUEST_HANDLER
ErrorCode   The operation completed successfully. (0x0)

This is what SoapUI gets back:

HTTP/1.1 500 Internal Server Error
Cache-Control: private
Transfer-Encoding: chunked
Content-Type: text/xml; charset=utf-8
Server: Microsoft-IIS/7.5
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Fri, 18 May 2012 01:00:14 GMT

Where else can I look to find out what's causing this error 500? Extensive googling has yielded nothing useful. Or is this error familiar to anyone?

I should mention that browsing to the .asmx successfully yields the usual "The following operations are supported. For a formal definition, please review the Service Description" page, and both SoapUI and my .NET WCF client were able to retrieve the WSDL from that URL to build their proxies.

Solution

Oh, man, sometimes all it takes is a drive home, a dinner, an evening with the kids, and a Stackoverflow post.

I suddenly recalled a similar and totally mysterious problem I had on some older version of Windows a long time ago: all I had to do was install or enable something that I was appalled to find wasn't installed and enabled by default. And indeed, I went into Programs and Features, Turn Windows features on or off, and browsed to Internet Information Services/World Wide Web Services/Application Development features, and selected checkboxes next to .NET Extensibility and ASP.NET.

Features Required

Now I'm getting a beautiful SOAP response back.

-1, massive fail, boo, un-like, etc. to Microsoft for still not allowing this error to be more transparent.