Alternating failure on long request executions

[Brad Wood]

<environment>
Consuming a web service from a VS2005 beta 2 test harness on WinXP. Web
service built with VS2003 running on my machine with IIS 5X set to use
ASP.NET 1.1
</environment>

I have a web service that creates a thread for each request in an input
document. Each thread then makes an HttpWebRequest.GetResponse call.

When only one request is submitted in the input doc all is fine.

When several requests are sent in the input doc, the call to the service
takes over 2 minutes to complete. In these cases everything works fine
on every other attempt (success, failure, success, failure). When it
fails, ASP.NET returns:

"The XML file [path to machine.config] could not be loaded. Attempted to
access an unloaded AppDomain."

Most previous threads related to this problem had to do with unmanaged
C++ extensions in .net 1X. I tried increasing the
responseDeadlockInterval attribute in machine.config.

It sure seems to be related to ASP.NET behavior on long request
executions, but I don't know what else to look at...

<stackDump>
[AppDomainUnloadedException]: Attempted to access an unloaded AppDomain.
at System.Threading.Thread.SetCompressedStackInternal(IntPtr
unmanagedCompressedStack)
at System.Threading.Thread.SetCompressedStack(CompressedStack stack)
at System.Xml.XmlTextReader.CreateScanner()
at System.Xml.XmlTextReader.Init()
at System.Xml.XmlTextReader.Read()
at System.Xml.XmlReader.MoveToContent()
at System.Web.Configuration.XmlUtil.OpenXmlTextReader()
at System.Web.Configuration.HttpConfigurationRecord..ctor(String
filename, HttpConfigurationRecord parent, Boolean inheritable, String
path, String mappedPhysicalPath)
[ConfigurationException]: The XML file [machine.config] could not be
loaded. Attempted to access an unloaded AppDomain. ([machine.config])
at
System.Web.Configuration.HttpConfigurationSystem.CacheLookup(String vpath)
at
System.Web.Configuration.HttpConfigurationSystem.ComposeConfig(String
reqPath, IHttpMapPath configmap)
at System.Web.HttpContext.GetCompleteConfigRecord(String reqpath,
IHttpMapPath configmap)
at System.Web.HttpContext.GetCompleteConfig(String path)
at System.Web.HttpContext.GetAppLKGConfig(String name)
</stackDump>