IIS serves ASPX but not ASMX

Deployed an ASP.NET webforms application to IIS 6.0 64-bit server. Some associated DLLs are only available in 32-bit so I enabled 32-bit applications following these instructions. At first I was not able to view ASPX pages but I had forgotten to Allow the ASP.NET Web Service Extension. Sorted!

Recent testing has shown that a 404 is received when requesting ASMX web service files. From the IIS log the status code is:

404 0 2

Anyone have any ideas? I anticipate this being something silly like all 404开发者_JAVA技巧s.

UPDATE 1

Not sure if this is related but the same error code is received when requesting PNG files. No problem serving JPG or GIF from the same folder... what!!!??? It is worth noting that if I change the extension of the image to JPG then it can be requested.

UPDATE 2

See answer below.

Okay found the problem.

C:\WINDOWS\system32\inetsrv\urlscan\UrlScan.ini did not have the PNG and ASMX extensions specified in the AllowExtensions list.

A nice quirk in our IIS server build!

Have you made sure that for .asmx file types, the handler is mapped to asp.net dll and that "check if file exists" is unticked within IIS?

I have changed connection pool to "Classic" from integtrated and it started working for me