Most of the errors I was seeing in the xterm, disappeared when I did it that way. One web page I found, said this was because a second Xserver was being invoked.

There is still one error that appears when I try to run some remote apps.

It seems that there is an Xlib extension named RandR (rotate and resize) which the error claims is missing. Not sure if that means it's missing on the Ubuntu box or the Mac.