I upgraded SP 2010 Solution created using VS 2010 to SP 2013 solution in VS 2012. The Solution has one SharePoint project which references another SharePoint project in the same solution. There are "using statements" in the project which refer to classes in the referred project. When I build individual projects or whole solution everything builds fine. However, when I try to deploy or package a project which references another SharePoint project, I get the namespace error:

The type or namespace name 'XXXXX' does not exist in the namespace 'XXXXXX' (are you missing an assembly reference?)