Matrix inversion problem

The following matrix fails to invert, unless bigfloats are replaced with
rats,
with keepfloat:true;
The error message is:
Maxima encountered a Lisp error:

 -: $POS is not a NUMBER

matrix([2.5B-1*s+4.0B-2/k1,-4.0B-2/k1,0,0,0,0],

[-4.0B-2/k1,2.0B1*s+4.0B-2/k1+4.0B-2/(1-k1),-4.0B-2/(1-k1),0,0,
               -2.0B1*s],

[0,-4.0B-2/(1-k1),2.0B1*s+1.0B-2/k2+4.0B-2/(1-k1),-1.0B-2/k2,0,

0],[0,0,-1.0B-2/k2,2.0B1*s+4.0B-1/k3+1.0B-2/k2,-4.0B-1/k3,0],
              [0,0,0,-4.0B-1/k3,4.0B-1/k3+4.0B-1/(1-k3),0],
              [0,-2.0B1*s,0,0,0,2.0B1*s+1.0B-2])

Determinant succeeds here, so the problem seems to be bigfloat related.