Running SU 2016 Pro 64-bit on Win7, when I double click on a .skp file I get an error that says it is not a Sketchup file. I cannot run Sketchup and load a file either - same error! Files were saved from SU 2015 and 2014.
I uninstalled SU 2016 and installed SU 2015 and have the same problem. The error reads, “! This does not appear to be a SketchUp model!”
A possibility is that Windows is still linking your .SKP files to an older version of SketchUp. What you could try is to open SketchUp 2016 first, and then open the files from within the program. This should also fix the association problem for the future, although it might not be 100% certain. Another way is to right-click on the file in Explorer - the contextual menu should show the available SketchUp versions.