I have a quite similar problem with this support discusson :
We use New Relic but I stopped the service before trying to run dotTrace. New Relic is stopped because I don't see anything on their interface.
As I stopped New Relic, I've restarted IIS. When the website was restarted, I ran then dotTrace. It has worked twice. Five hours later, I became the warning message below when I tried to re-run dotTrace.
What do I need to do ?
I can't restart the website in the daylight because of our traffic (250k session/week).
The idea to use dotTrace was to run (on demand) it as we are facing problem with the website.