The xset command appears to be buggy in Ubuntu. $BIRCH/script/birchace.py contains the line:

subprocess.call(['xset', '+fp', ACEFONTS], env=ACEENV)

which adds a directory to the font path. This works on all other Linux, OSX and Solaris platforms, but not on Ubuntu.
On Ubuntu, we get the message:

xset: bad font path element (#1), possible causes are:

Further experimentation with this line appears to show that none of the prescribed fp options (eg. +fp=, fp+=, fp=)
seems to work, even when typed at the command line. It seems likely that this is a bug in the xset command in Ubuntu.

Consequently, no of the xace programs can run.