When Spectre emits this message it suggests you have a nonlinear capacitor model that is discontinuous.

The warning is emitted when Spectre has run into a convergence problem in transient. Such problems are often due to discontinuities in the device models. When there is a discontinuity in the device model it could be in the resistive part of the capacitive part. When the simulator encounters a discontinuity it will start by shrinking the time step. This generally helps if the discontinuity is in the resistive part of the model because as the time step shrinks the effect of the capacitive part of the model tends to dominate over the resistive part, effectively smoothing the discontinuity. If there is no capacitive part of the model, you can get the same effect by specifying cmin. However, if the discontinuity is in the capacitive part of the model, shrinking the timestep is the wrong thing to do. If Spectre is not able to achieve convergence by shrinking the step in transient analysis it will instead try growing the step. However, normally the stepsize is bounded by the constraints on the Local Truncation Error, thus it cannot grow the step without violating the LTE criteria. This could affect the accuracy of the result, so it prints the warning message if it is successful in converging by growing the step beyond what normally would have been allowed. If you look carefully at the waveforms at that point in time you will see the simulator took a large step and you can judge whether to trust the simulation results or not.

-Ken