This bug has been reported on Ubuntu Launchpad as: 
https://bugs.launchpad.net/bugs/539247



These are the lines that appeared in the .xsession-error files:

<stdin>:1:3: error: invalid preprocessing directive #Those
<stdin>:2:3: error: invalid preprocessing directive #or
<stdin>:3:3: error: invalid preprocessing directive #Xft
<stdin>:4:3: error: invalid preprocessing directive #Xft

These "warnings", not errors, can be eliminated if the # is replaced by ! for comment lines in the

/etc/xdg/xfce4/Xft.xrdb

file as indicated in the xrdb man page.