Had to remove reference to "Callisto.." from the References Node and had to go to Nuget and reinstall Callisto, now the Solution Builds fine.
Downloaded the code from the codeplex site, opened the solution and did a "Build" and got the following error and warning
Error 1 Could not find SDK "Callisto, Version=1.2.1". Expenses
Warning 2 The referenced component 'Callisto' could not be found. Expenses