I have created an add In using VS2013 with targeted framework 4.5. Its working fine in Outlook 2013 (System spec: Windows 8.1, Visual studio 2013 and office 2013).
But when I try to use the same in Outlook 2010 I am getting an error message "The common language runtime could not be loaded by (add in path). Contact your administrator for further assistance.". I have installed required .net framework and Microsoft visual studio 2010 tools for office runtime (Testing machine with windows 7 and office 2010).