Steepest Descents:
Tolerance (Fmax) = 1.00000e+03
Number of steps = 50000
Step= 0, Dmax= 1.0e-02 nm, Epot= 6.71345e+30 Fmax= 8.76006e+06, atom= 5810
Step= 1, Dmax= 1.0e-02 nm, Epot= 2.11041e+16 Fmax= inf, atom= 5819
Step= 15, Dmax= 1.5e-06 nm, Epot= 2.11041e+16 Fmax= inf, atom= 5819
Energy minimization has stopped because the force on at least one atom is not
finite. This usually means atoms are overlapping. Modify the input
coordinates to remove atom overlap or use soft-core potentials with the free
energy code to avoid infinite forces.
You could also be lucky that switching to double precision is sufficient to
obtain finite forces.
I had the same problem, and upon visual inspection, parameters/coordinates look fine, but in EM, they acquire an unusual bonding pattern. Later, I refined these things and simulated the complex successfully...