unable to find a register to spill in class 'NO_REGS' appears when I'm building my model for my arduino

I have made a model for controlling my heating elements with a PWM. Because I wanted to measure my temperature of my elements, I also created a S-Function-Block for a SPI-Bus-System (it works actually in the Arduino IDE and the Block works also for several thermocouples). If I start the whole model for the heating elements and the temperature I'm getting the Error from the headline above and I don't know why....

I tried to change some timings but this didn't work, I also have changed the solver from ode3 to ode8 like I've read in some other posts, but I still have no solution...