To start multiple sessions of TIBCO Spotfire S+ running on the same machine, use the flag /MULTIPLEINSTANCES.
This can be added to the Target: line of your S+ shortcut icon in Windows. Every time the modified shortcut is clicked, a new instance of S+ will open. To set this flag, right-click on your S+ icon and select "Properties". Scroll to the end of the Target: line, add a space, and then ‘/MULTIPLEINSTANCES'. The target line would then read:
For S+ 6.2 "C:\Program Files\Insightful\splus62\cmd\SPLUS.exe" /MULTIPLEINSTANCES
For S+ 7.0 "C:\Program Files\Insightful\splus70\cmd\SPLUS.exe" /MULTIPLEINSTANCES
For S+ 8.0 "C:\Program Files\Insightful\splus80\cmd\SPLUS.exe" /MULTIPLEINSTANCES
For S+ 8.1 "C:\Program Files\TIBCO\splus81\cmd\SPLUS.exe" /MULTIPLEINSTANCES
Click "Ok" to apply the settings and close the dialog box. You will need to do this to all icons you use to start S+.