Dear njuxyh,
That is one of the important parameters that determines the accuracy of a finite bias calculation, but normally the default is quite safe (assuming that you are using FHI pseudopotentials). If the SCF cycle of your NEGF calculation gets very close to convergence, e.g. the variation in the Hamiltonian oscillates around 10^-3 eV (the default threshold for convergence is 10^-4), increasing the number of energy points can help.
On the other hand, if your SCF cycle blows up completely, it normally means that there is something else which goes wrong. For example, the density matrix used as an initial starting guess is not good enough, or that the bias you are applying is too large for your system. Of course, these are just guesses, it is difficult to say more without seeing the actual input.
Feel free to attach the input here or send it by mail if you need further assistance.
Regards,
Daniele.