@Rita, go to Simulation->Configure simulators and tools, remove the -a option to the ngspice command line (-a is for autorun), the linearize command will work without warnings. I don't know why the -a option causes this issue. From my understanding ngspice run with -a option will start simulation if circuit contains no .control / .endc sections (for example a .tran 0,1n 500n is used). However if circuit contains a .control section simulation is started anyway. Using -a option will cause trouble in this case.