It is hard to say when all we have is just the error message.
However, from the error message, it tells that something apparently created very large forces in the simulation and yielded a very high velocity. That can happen either when the time step is too large, or when particles overlap very much.
You said that you reduced the time step, but the error still occurred. How much did you reduce the time step? As a suggestion, start with making the time step really small, like 0.001 times the time step you had so far, and try again. If it works now, you can increase it again.
Another thing to look for is the initial forces. How did you set up the system? If you set up the system randomly, there is a good chance that some particles are very close to each other. Depending on the interaction potential that you use, this might result in very large forces. To get rid of these large initial forces, you can use a warm-up with force capping (inter forcecap) to get the system to a state where these large forces disappear.
Olaf