1. Make certain that the .less files are marked as Content in VS
2. Make certain that its not a less compilation problem. Do this by running the dotless compiler manually from the command line.
3. Perhaps you need to add the .less mime type mapping in IIS / your web config file:

 

<system.webServer>
  <staticContent>
    <mimeMap fileExtension=".less" mimeType="text/css" />
  </staticContent >
</system.webServer>

This one is for TC agents…

From: http://www.xinotes.org/notes/note/1066/

To grant a user “logon as a service” right on Windows 7:

1. Enter secpol.msc into the “Search programs and files” box (the Run box for previous Windows versions) and press enter.
2. Locate “Local Policies” and “User Rights Assignment”, then double click “Logon as a service” in the right panel.
   
3. Add the user or group