I have been facing the problem with a Windows7 installation of Octave. However, the bug report link that is quoted everywhere (quoted below) is dead. Please send me the bugfix. I have faced this problem once before, and remember having used a fix in form of building or installing some package from Octave command line.
"When plotting Octave occasionally gives me errors like `gnuplot> 9 0.735604
line 26317: invalid command'.