That's odd. Here is a quick work-around. Create an empty folder somewhere and select it as the upgrade path. After the installer is done, manually copy the contents of the new folder to the actual Jamstix 2 location and let it overwrite.
Hmmm....your suggestion helped....perhaps it was user (my) error....when I select a folder the installer automagically appends "/Jamstix2" on the end so I realized the reason it wasn't working is that the file path had 2 "Jamstix2" folder paths...for example:
Because the second "Jamstix2" folder did not exist I believe that is why I was getting the pop up error. I took one of the "Jamstix2" out of the path name and the install worked fine.