CCS v6.1.2.00015 does not import a project using an older compiler

Please see this wiki article for the explanation of why project imports may fail: 
http://processors.wiki.ti.com/index.php/Importing_CCS_Projects

You would need to install the exact compiler version that the original project was created for. You can do that by going to menu Help->Install New Software, select "Code Generation Tools Updates" from the Work With list, uncheck the box "Show only the latest versions...", then expand TI Compiler Updates, and select and install the specific version that you need.