I followed the instructions in this link: http://msdn.microsoft.com/en-us/library/bt727f1t.aspx to install the remote debugger (2012) on my server where the application is runni
It turns out the one thing I missed was to tell Visual Studio where to find the .pdb symbols relating to the remote process. To do this go to Tools -> Options -> Debugging then in the Symbol (.pdb) locations add the remote location to the pdb files.
To clarify, I was attaching fine but could not break into code. Now I can. Be aware though that there are other hurdles before you get to my stage where I was attaching to the process successfully but could not catch a breakpoint.