I installed jhandles and it showed different error.
FYI my OS was windows XP.
-----------------------------------------------------------------------------------
- Graphics backend: jhandles.
octave:1> x=chirp([0:.001:2],0,1,150);
octave:2> specgram(x,256,1e3,256,250);
error: index exceeds N-d array dimensions
error: evaluating argument list element number 1
error: evaluating binary operator `/' near line 22, column 62
error: evaluating argument list element number 1
error: evaluating argument list element number 4
error: evaluating assignment expression near line 21, column 11
error: called from `image' in file `C:\Program
Files\Octave\share\octave\packages\jhandles-0.2.0\image.m'
error: evaluating if command near line 106, column 3
error: called from `imagesc' in file `C:\Program
Files\Octave\share\octave\2.9.12\m\image\imagesc.m'
error: evaluating if command near line 171, column 3
error: called from `specgram' in file `C:\Program
Files\Octave\share\octave\packages\signal-1.0.1\specgram.m'
--------------------------------------------------------------------------------------------------