All, after two hours of faffing about. Here is the solution...
You may already have Dotfuscator 4.9 (build 4.9.8500_2.0) installed, but VS2012 will not recognise this installation (the relevent VS2012 addin will not be 'linked' with VS2012). I first tryed a complete uninstall of Dotfuscator
and reinstalled, suprisingly this did not work on a Sony VAIO running Windows 8, but did on a Windows 7 machine - this may have been an anomoly. To get the Dotfuscator project type in VS2012 on the Windows 8 system, I did not uninstall Dotfuscator, but merely reran the install package - this seemed to work.
I hope this saves someone else a couple of hours.