Thanks for the response Ayman. I am actually not applying external forces. I'm simply running inverse dynamics to solve for joint torques after inputting a motion file.
To give more specifics... I have an arm body connected to a clavicle body that is connected to a torso body and then the torso is connected to ground. I have specified motions for all DOF related to the arm, clavicle and torso. The torso has rotational and translational DOF. I get the previously stated error when I try to run inverse dynamics as is, however I do not get the error when I connect the clavicle directly to ground or remove the translational DOF of the torso body entirely from the model (not just the motion file). Any idea why this would occur?
Thanks again,
James Buffi