Simulink error, STM32-MAT package, Function call from timer interrupt

I am following the tutorial that comes with the STM32-MAT package that deals with setting a basic block diagram to run on an STM32 target. In the simulink system I have used the predefined STM32 timer block and set it up at a frequency of 1Hz and to output an interrupt (UP) every second. The output of this block (IRQ UP) is fed as the trigger for a function call block in which I simply toggle a GPIO pin (again with the predefined STM32 GPIO_WRITE block provided in the package).

I have my code generation set to stmtlc and simulation type to 'normal'. I have set up the STMioc file with the necessary timers, interrupts and gpio ports. When I run the simulation I get an error:

An error occurred while running the simulation and the simulation was terminated Caused by: Function-call initiator 'untitled/Timers' attempted to reenable function-call subsystem 'untitled/Function-Call Subsystem' on time step '0.0'. The function-call subsystem cannot be reactivated by the same function-call initiator; there is a flaw in the implementation of the function-call initiator.

I dont understand what the issue is here.