IIRC, you are recommended to have Poser & core run-time on C: lest sundry legacy scripts, modules etc fail to 'play nice'. Same caution applies to other CAD programs: If core is not on C:, all bets are off...

I've a minimal 'runtime' on default C:, just core Poser. External library calls utilities and WIP stuff from my ½T archive on E:, calls I 'unload' when done. Archive is reasonably organised, each of the many, many sub-sets with its own mini-run-time...