I just got bit by the latest service pack release.  Updated my SolidWorks to 2016 SP2 and it automatically updates my PDM professional client to SP2 as well.

Now lo and behold, I cannot connect to the 2016 SP1.0 PDM server because the versions are now incompatible...

Unfortunately, upgrading the server is no easy task here.

Service packs should prompt you IF you want to upgrade and or give a strong warning before upgrading....