cadence xval()
For your first error, there is some CDF call back function working in the background that will try to calculate some parameter like Perimeter of Drain region or area of drain region. When you dont enough parameters for that callback function it displays an error in the schematic window. To confirm about your simulation you need to look at your netlist that every parameter of your interest is existing there. Generally for RF simulations where S parameters are observed, the parasitic and fringe capacitors also matter and hence PD,PS,AD,AS parameters sometimes change those low capacitance values appreciably.
For your second error, as far as I know your S parameters are calculated from the values you give after a simulation. The equivalent ac circuit or equation parameters are stored inside and after you gave sweep values etc, the tool calculates the response and plots it. But when you run the new simulation the buffers are emptied which hold your previous simulation results and pointers to results. Hence when you try to Refresh such addresses are invalid and point to nil. Hence you need to start from again from the beginning of your results display window again. Refresh probably cannot work here.