Please trying rebuilding your application and then run.
If that doesn't work, please kill all processes like WebDev.WebServer in task manager & then run.
If that doesn't work too, try solutions mentioned at:
http://forums.asp.net/t/1583577.aspx[
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webdev.webserver.exe[
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adding/removing a file in VS2010 causes "WebDev.WebServer20.exe has stopped working" error