I know it’s kind of late for the OP but I ran into the same problem while trying out the Bootstrap 3 for MVC 4 NuGet package, in my case it had something to do with the Microsoft.AspNet.Web.Optimization package, and managed to find a simple solution.
Try executing the following commands in the package manager console:
Install-Package Microsoft.AspNet.Web.Optimization
Update-Package WebGrease
Uninstall-Package Microsoft.AspNet.Web.Optimization
Uninstall-Package WebGrease
Install-Package Microsoft.AspNet.Web.Optimization
Update-Package WebGrease
The first two lines had no effect for me since those packages were already installed and updated by the Bootstrap 3 for MVC 4 package, but I ran them anyway and then it all compiled and ran great.