If someone got the same Simulink Coder Fetal, and particularly on utillib.tlc, which leads to no fully build you code.
"Simulink Coder Fatal: Start time must be 0.0 for the chosen target: 1.0."
In 'Configuration Parameters', in 'Solver' the 'start time' is 1 or something else it must be '0.0'. and recommended to change the other settings, make the Solver auto and fixed-step size to '0.01' or '0.1'.
"Simulink Coder Fatal: Custom is attempting to create file main, however, this file was already created by Simulink."
You just need to change the Simulink file name probably you named it like main.slx which leads to creating this Error. Just close the file, change the name to anything else and compile and build it again, it will work. For some MCU you need to Update the path, in 'Configuration Parameters', on MCU options under 'Code Generation' click 'update installed path'.