Hi . . . I am suddenly getting these errors as well, on my first build attempt since upgrading to 5.6 / 1.8.4.
@jeanfabre, you say above to select the 1.8.4 package -- it seems that in the zip I downloaded, they are ALL 1.8.4, but for different versions of Unity, and with the most recent version being 1.5.4.
Did you mean pick the 1.5.4 version, or should there be one specifically for 1.5.6?
Thanks!