I would install the newest TeX Live
over the internet, not the Ubuntu version from 2009. Perhaps this solves the issue. Furthermore, there's a script called
getnonfreefonts which you could use.
Regarding
\nullfont, from the TeXbook:
The primitive control sequence \nullfont stands for a font that
has no characters. This font is always present, in case you haven't
specified any others.
Please show a small
minimal working example, which produces this error, so we see which packages and which settings are involved. Furthermore, please post your .log file.
Stefan