I have written a very simple scheduler client, which is intended to update when the application comes online, and which appears to work fine when it is called every few minutes, but if you attach it to the APPLICATION_STARTUP event in timer mode, it causes exactly this kind of error. I t appears that on application startup, my scheduled task is called repeatedly; running in debug mode, I can see that every time it finishes, it seems to be called again, and this endless repeated call seems to be the cause of the hang. If I switch to request mode, my client is called every single time the page changes, which is quite an overhead for something that needs running just on application startup. I have no idea what to do to stop the hang happening, but any suggestions would be more than welcome.