Problem with eigenvalues



I'm using wxMaxima 0.8.4 with Maxima 5.20.1.  I ran into a problem when 
calling eigenvalues (and so eigenvectors, too):

I am simply trying to get the eigenvalues for a 6x6 Laplacian matrix (-R6) :

R6:matrix(
[-16,10,1,1,3,1],
[10,-(18),1,2,1,4],
[1,1,-(2+3*8),8,8,8],
[1,2,8,-(3+3*8),8,8],
[3,1,8,8,-(4+3*8),8],
[1,4,8,8,8,-(5+3*8)]
);

eigenvalues(-R6);

The last command gives the following:

part: fell off the end.
#0: 
eigenvalues(mat=matrix([16,-10,-1,-1,-3,-1],[-10,18,-1,-2,-1,-4],[-1,-1,26,-8,-8,-8],[-1,-2,-8,27,-8,-8],[-3,-1,-8,-...)(eigen.mac 
line 94)
 -- an error. To debug this try: debugmode(true);

eigens_by_jacobi(-R6)  works OK.

Am I doing something wrong?

Thanks,
Dustin