Singular error when putting a current source in series with a capacitor (ngspice)
SPICE simulations begin by finding a d.c. solution at t=0. At d.c. the current through a capacitor is zero so there is no solution for a non-zero current source in series with a capacitor. Change your constant current source to a source that has an initial value of 0.0A and then ramps up quickly to the desired value.