Hi Luis,
I guess you ask yourself for this font in your .rootrc by a line like this:
May be your problem goes away by replacing “adobe” by “*”
If not:
what gives the command:xlsfonts -l -fn "-adobe-helvetica-medium-r-*-*-10-*-*-*-*-*-iso8859-1"
The font should be in the ubuntu package xfonts-75dpi
Cheers
Otto