WebDAV & Exchange 2003 - Works In Debug, Fails Without?

I am writing some code in VB.Net under .NET 2.0 which interfaces with MS Exchange 2003.Because of the Exchange 2003 "requirement" I am forced to write this code using WEBDAV.The code itself is replicating, to some degree,a schedule management process.It's creating Appointments on the Exchange Server in response to inputs from the user and managing it's data internally in a SQL Server database.The problem situation is this: A new person is assigned to be in charge of a meeting. The requirement says the program should generate a meeting cancellation request to the person removed from the meeting (if such a person existed) and a meeting request sent to the new person.In the case of there being an existing person, what appears to happen is this:

The meeting cancellation request

gets sent Exchange barfs and returns status code 500 (internal server error) during the set of requests which send the meeting request to the new person.However! While debugging this particular scenario, it works just fine for me, if I step through the code in the Visual Studio debugger. Left to it's own devices, it fails every time.Just for yuk's sake, I added a Thread.Sleep(500) to the part after sending the cancellation request, and Exchange doesn't barf anymore...

So, my question! If adding a Thread.Sleep to the code causes this error to go away, a race condition is implied, no? But, my code is running under a web application and is a totally single threaded process, from start to finish. The web requests I am sending are all in synchronous mode so this shouldn't be a problem. [code]....

...but a lot of the implementation details are hidden here, as I wrote a set of classes to interface with Exchange WebDAV.