unix() error: unable to start subprocess

[Alois Schloegl]

I'm analyzing a number of data sets, within the analysis of each data set calls the 
function unix('grep ...'). After about 7 hours and successfully analysing a number of data sets (in my case its 53), the batch suddenly stops with the error 
   error: unable to start subprocess for `grep ...'
   error: called from:
   error:   /usr/local/share/octave/3.3.52+/m/miscellaneous/unix.m at line 38, column 21

The bug is not triggered when unix(...) is called within a simple loop. Therefore, it is very difficult to debug this problem. Can anyone explain which conditions can trigger this situation? 

If the problem is caused by some memory leak in some subfunctions used by the analysis routine, what is the best way to track down the problem ? 

This was observed with Octave v3.3.52+ compiled on 2010-09-21 from the sources.

Kind regards, 
    Alois