What am I missing? I upgraded to ArcGIS 10.3 succesfully recompiled all other 20 or so addins after encountering a similar issue and renaming "ESRI.ArcGIS.AddIns.11.targets" to "ESRI.ArcGIS.AddIns.targets" possibly due to a known defect (#01599069)
Now I would like to create a brand new addin but I get the same warning. If if rename "ESRI.ArcGIS.AddIns.targets" back to "ESRI.ArcGIS.AddIns.11.targets" the warning dissapears and addin seems to compile but none of my old addins will recompile raising the same old error.
If i copy and paste the "ESRI.ArcGIS.AddIns.targets" and also keep the "ESRI.ArcGIS.AddIns.11.targets" both the old and new addins compile without errors or warning but the new addins ref ID are not recognized by the older upgraded addins.
I am pretty much completely confused as to what needs to be done here to make this work.