[R] R 'could not find any X11 fonts'

[fsando]

I'm having this problem - and I have seen earlier post on the same 
problem - but the solutions either do not work for me or (being fairly 
new to linux) I do not understand the suggested actions.

So here goes:
Whenever I try to add a 'main' title R responds with an error that it 
can't find any X11 fonts.

### Very basic examples ###
# 1. No error (a scatterplot x=1:10 and y=1:10):
plot(1:10,1:10)
# 2. No error (as above, but add a subtitle):
plot(1:10,1:10,sub="subtitle")
# 3a. Error (as above, but add a main title):
plot(1:10,1:10,main="Main title")
# 3b. Error (an equivalent way to produce the same):
plot(1:10,1:10) # no error
title(main="main") # error

# produced error:
 > plot(1:10,1:10,main="main")
Error in title(...) : could not find any X11 fonts
Check that the Font Path is correct.

# output from sessionInfo()
 > sessionInfo()
Version 2.3.1 (2006-06-01)
i486-pc-linux-gnu

attached base packages:
[1] "methods"   "stats"     "graphics"  "grDevices" "utils"     "datasets"
[7] "base"    

# I don't know if this is relevant but
# from getOption("X11fonts")
 > getOption('X11fonts')
[1] "-adobe-helvetica-%s-%s-*-*-%d-*-*-*-*-*-*-*"
[2] "-adobe-symbol-medium-r-*-*-%d-*-*-*-*-*-*-*"

### examples end ###

The solution may obvious for somebody more familiar with Linux, but as 
stated, I'm new to Linux, so I would appreciate detailed explanations.
Thanks