I'm getting the same issue.
Client (on Windows 10) apparently automatically updated to 1.9.1 this morning.
Updated my local servers because the 1.9.1 client wouldn't connect to the 1.9.0 servers.
Joined one of the servers.
Got into a boat.
Got kicked with the above exception.
Now get immediately kicked with the same exception every time I connect.
Have tried restarting client and server multiple times.
The above workaround (1.9.1-pre3 client) worked with my local servers.
At least it allowed me to connect and get out of my boat.