Thank you very much, to you and Dave. That is the problem as you have described. We were able to correct it and now can successfully launch SketchUp on my son's Mac. Happy New Year to all!

We are trying to open a .skp file. When we attempt this we are asked for a location to expand the file and an expander icon appears on the desktop. We set the location in our documents folder and say ok, then get an error message that the stuffit engine is unable to determine the file format. Thank you for your help.

I am trying to install Sketchup on my son's Macbook Pro, which is running OSX 10.9.1. We are able to install the application and save a file, but then when trying to launch the saved file, we get an error message that file cannot be opened. We tried to install both Sketchup version 8, the one he uses at school on a PC, and also version 2013 for Mac. Both give us the error message when opening files. Any advice appreciated. Thank you.