The message is clear:  no, you can't use two docks simultaneously.  
I have TWO Dell WD19TB docking stations  - I have one Dell XPS 17 9700 laptop - When I connect both WD19TB to this single XPS 17, while booting the system gives an error "Multiple Docking Stations Not Supported - Disconnect one of them" and stops booting up further. When I disconnect one WD19TB, the XPS 17 boots normally. How can I use these TWO WD19TB docking stations with this single XPS 17 9700 laptop? Thanks in advance for your help.
Multiple Docking Stations Error on POST Boot