Unknown server tag 'webopt:bundlereference' error while publishing Web Forms application using VS2013

Hello,
While publishing the web forms application using VS2013 I am getting 2 errors repeated several times. These are:
1. /Site.Master(14,0):Error ASPPARSE: Unknown server tag 'webopt:bundlereference'.
2. /Site.Master(20,0): Error ASPPARSE: Unknown server tag 'ajaxToolkit:ToolkitScriptManager'.
I have tried the following taking a cue from http://stackoverflow.com/questions/17130988/unknown-server-tag-weboptbundlereference
1. Publish in Release version instead of debug
2. debug=false in web.config
3. Nuget package Microsoft.AspNet.Web.Optimization.WebForms is already in the solution
4. web.config reference is already there -
      <controls>  &nbs ...