This looks like a bug (A12-140)

[Bill Daly <bill@wmdaly.com>]

Version 2.4.2 for Windows gives me this:

   facq1 = nffactor(nfq1, q1);
   rootsq1 = -subst(lift(facq1[,1]),x,0);

'facq1' is a 24*2 matrix (the output of nffactor), but 'rootsq1', which 
should be t_COL [24,1] is instead t_VEC [1,24]. This is in the middle of 
a longish piece of code, so it wouldn't surprise me if it's sporadic. 
(It's easy enough to work around, but it looks sort of dumb.)

Regards, Bill