Easy: one or more of your tests are throwing StackOverflowException or maybe other fatal error the system is not able to recover from. Infinite recursion causes this.
TestDriven.Net might print this in the output window: "An existing connection was forcibly closed by the remote host"
To find out which one, run all the tests with Resharper and see which one is "aborted". Then add a break point and debug it. The debugger will tell you exactly where is the problem for you to fix it.
Happy testing! 🙂