While you can run two or more versions at the same time do not try to render at the same time as it will cause a conflict between resources.  Also if you use the Queue Manager be aware that they only work with a specific version of Poser and you have to use the Exit option to fully shut it down.  Just clicking the Upper X makes it disappear however it is still running and if you run Poser 11 QM then work with Poser 12 it will give weird results. 

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13