"Invalid file name for monitoring" rewrite querystring

[Brian]

I've deployed a 'URL rewriter' version of our application almost two
months ago and it is working great (.NET 1.1, Win2k, IIS5). Since then,
I've gotten just FOUR exceptions that look like this:

The description for Event ID ( 0 ) in Source ( Application ) cannot be
found. The local computer may not have the necessary registry
information or message DLL files to display messages from a remote
computer. The following information is part of the event:
Exception: HttpException
MESSAGE: Invalid file name for monitoring: '[...local
path...]\search.aspx?Make=Ford'. File names for monitoring must have
absolute paths, and no wildcards.
SOURCE: System.Web
URL: http://www.[...my server...].com/search.aspx?Make=Ford
FORM:
QUERYSTRING:
TARGETSITE: System.String GetFullPath(System.String)
STACKTRACE: at System.Web.FileChangesMonitor.GetFullPath(String
alias)
at System.Web.FileChangesMonitor.StartMonitoringPath( String alias,
FileChangeEventHandler callback)
at System.Web.Caching.CacheDependency.Init(Boolean isPublic, Boolean
isSensitive, String[] filenamesArg, String[] cachekeysArg,
CacheDependency dependency, DateTime utcStart)
at System.Web.Caching.CacheDependency..ctor(Boolean isSensitive,
String[] filenames, DateTime utcStart)
at
System.Web.Configuration.HttpConfigurationSystem.G etCacheDependencies(Hashtable
cachedeps, DateTime utcStart)
at
System.Web.Configuration.HttpConfigurationSystem.C omposeConfig(String
reqPath, IHttpMapPath configmap)
at System.Web.HttpContext.GetCompleteConfigRecord(Str ing reqpath,
IHttpMapPath configmap)
at System.Web.HttpContext.GetCompleteConfig()
at System.Web.HttpContext.GetConfig(String name)
at System.Web.HttpRequest.get_ContentEncoding()
at System.Web.HttpRequest.FillInQueryStringCollection ()
at System.Web.HttpRequest.set_QueryStringText(String value)
at System.Web.HttpRequest.InternalRewritePath(String newFilePath,
String newPathInfo, String newQueryString)
at System.Web.HttpContext.RewritePath(String filePath, String
pathInfo, String queryString)
at Insignia.Catalog2.ModuleRewriter.RewritePath(HttpA pplication app,
String path)
at Insignia.Catalog2.ModuleRewriter.Rewrite(String requestedPath,
HttpApplication app)
at
Insignia.Catalog2.BaseModuleRewriter.BaseModuleRew riter_BeginRequest(Object
sender, EventArgs e)
at
System.Web.SyncEventExecutionStep.System.Web.HttpA pplication+IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionS tep step,
Boolean& completedSynchronously)
HttpException: Code=500 HResult=-2147024809.

The IIS log entry is:

2006-02-18 14:53:09 217.169.46.98 - 192.168.20.248 80 GET
/ADW1/search.aspx?Make=Ford - 500 0 Mozilla/4.0+(compatible;) -

(I replaced real paths and URL's with [...])

Notice in the exception log entry that QUERYSTRING is empty - somehow
the QUERYSTRING isn't being detected and/or split from the URL.
Apparently the first arg to HttpContext.RewritePath() doesn't like the
query string. I can hit the same page myself and never get the 500
error. This site gets hundreds of thousands of hits each day. What
would make this request generate this error?

Thanks!

-Brian