As a simulation exercise, I am trying to work out a power supply and actually I am at the point provided in the figure below
There is a message of error which I don't understand, but I realized it happens only with the presence of the diode in the circuit.
In fact, in order to understand this, I did two other attempts: a separate circuit on the right with a diode which works fine and a short circuit around the diode itself which is reported in the next figure
and still it works fine.
So the question is: which is the problem with adding that diode in the circuit?