I have a web service running under IIS 6 on a Windows 2003 SP2 machine. Approximately 37% of the calls to this service (33K of 88K) result in a 400 error according to the IIS logs. There are no corresponding 400 errors in the httperr log however. We've also noticed that these errors originate with clients showing the same protocol and user agent combination in the IIS log:
| HTTP/1.1 |
MOZILLA/4.0+(COMPATIBLE;+MSIE+6.0;+MS+WEB+SERVICES+CLIENT+PROTOCOL+1.1.4322.2407) |
Interestingly, the same web service interface running on a W2K SP4 machine and IIS5 experiences 500 errors at a 70% rate from exactly the same protocol / user agent combination and the try/catch block at the top of the application does not report any uncaught exceptions.
In both cases, a small percentage of the calls using the same protocol / user agent combination do succeed.