I have an ASP.NET web application that uses Web Resources via the WebResource.axd handler to serve up some CSS for my site. The reason I use this method is because I can place the CSS in a .NET assembly and reuse it across several web applications which comes in handy when several sites need the same styling.
Everything was working fine until about a month ago. Then, I started noticing that when I deployed my website to production the styles were all messed up. But strangely, it would fix itself after a couple of minutes. It worked like a charm every time locally but not in production. Using Firebug I noticed that the calls to the WebResource.axd files were causing a 302 Redirect to GenericErrorPage.htm which obviously means something is going very wrong. I checked the Application event log in Windows but didn’t see anything.
After some fiddling around and pulling my hair our for a few hours, I changed the web.config so that debug=”true” and noticed some w3wp.exe errors show up in the event log.
Process information: Process ID: 4932 Process name: w3wp.exe Account name: NT AUTHORITY\NETWORK SERVICE Exception information: Exception type: ArgumentOutOfRangeException Exception message: Specified argument was out of the range of valid values. Parameter name: utcDate at System.Web.HttpCachePolicy.UtcSetLastModified(DateTime utcDate) at System.Web.Handlers.AssemblyResourceLoader.System.Web.IHttpHandler.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)</pre>
utcDate, UtcSetLastModified – huh?
Noticing the event log entry seemed related to dates in some way (utcDate, UtcSetLastModified, etc.) I took a look at the system clock on my build server (where the assemblies are built) and compared to my production machine. Sure enough, my build server’s clock was fast by about 5 minutes. After reading around I found that WebResource.axd uses caching and relies upon a querystring parameter (“t”) to determine if it needs to re-cache or serve from existing cache. If the request time parameter is in the future (dictated by your assembly build time), it gets confused and throws an exception.
Bottom line: Syncing the clocks on my build server and production server fixed the issue.