The Problem
You are coding away, Visual Studio locks up for one of it’s many reasons, and reopen your project and run it again. You then get the “Unable to launch the visual studio development server because port 9452 is in use” error
The Cause
When Visual Studio crashed, the Web Server did not, so basically it thinks you are trying to run two instances at the same time, which is not allowed.
The Solution
Open up the process manager, go to the Processes tab, and select “WebDev.WebServer40.exe” and click “End Process”. Then try running your project again. Visual Studio will now start the project fresh and the problem should go away.