I had finished taking some flats and clicked the X in the top right corner of the main window to exit SGP.
SGP said the sequence had changed and did I want to save it. I clicked Yes, then got this:
At that point I checked Task Manager to see if there was perhaps another instance of SGP running that might be accessing the .sgf file, but there was not.
I clicked continue and the app exited without further ado.
Log: http://adgsoftware.com/misc/03_sg_logfile_20150117232122.txt
Andy