If you're refering to a subVI, you should set to be reentrant in the File>>VI Properties>>Execution page.
You should consider the changes in functionality. You can find more about this in the LV user manual.
If you want the main VI to run twice, edit its INI file and add the line
AllowMultipleInstances=True
Although I'm not sure this will work for 6.0.
At most, you should be able to make a copy of the EXE and run it independently.
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