Two runtimes with the same extension on the datafile of the runtime can not be opened simultaneously. It causes a conflict. I ran into this in creating runtime tools for myself to use at work. When I create my runtimes, I give them different extension. I have had as many as 4 different runtimes going.
I am glad I talked my employer into purchasing FileMaker Pro for us.
Thank you for the response TKnTexas, could you please give me an example of the extensions you have used?
Instead of the suggested default of USR, you could use USR1, USR2, USR3 ...