I'm trying to play the Defense unlimited with my father, but can't get the multiplayer to work.
it says. "Cannot join. The following mod event handlers are not identical between you and the server. This indicates that the following mods are not multiplayer (save/load) safe. (see the log file for more detail):

mod-Wave_Defense_Unlimited"

The multiplayer works fine in the regular base defense.

Nay idea what the cause is?

With 0.16.9 I get the same error and can not play multiplayer. On the other hand, version 0.16.8 worked correctly.

should work now