Make sure that the two runtime solutions have different file extensions. You can leave one with the default .USR, but choose something different for the second runtime.
Your other option is to bind one executable file to both sets of solution files with the same binding key so that they are really one solution, not two.
Much obliged for your answer. I tried your suggestion with the different file extensions and it worked. Great stuff! Many many thanks!!
Re your other option, yes I could have one executable file for both sets, but they are not really related (the two solutions) - I was going to do this if I did not get an answer to my question. I find it strange that it worked on the Mac but not on PC (Windoze XP) - but I guess that is the "nature of the beast".
The two systems use different methods for figuring out what application to launch when a file is double clicked.
I haven't tried this, but I think you can keep your solutions separate but just use the same "bind key" as long as you open your solutions by double clicking the database file (or a shortcut to it) and not the executable. One executable will be ignored as the other will always be used to launch the run time application, but the correct file should open and function as expected--I think.