How can I set a subsystem containing s-function with as an atomic subsystem?

Hi, I have generated a s-function in simulink for my Amesim modell. The whole simulink modell should be running in fixed Step. I want to set the subsystem containing this s-function as an atomic subsystem, but were never successful. Error: 'test/vehicle/vehicle_plant_fixedStep_sfun' has an invalid sample time of [0, 0]. Periodic atomic subsystem 'test/vehicle' may contain only blocks that have constant (inf), inherited (-1), or periodic (0.0002) sample times. To resolve this issue, try to change the sample time with one of the following: - Configuring the block 'test/vehicle/vehicle_plant_fixedStep_sfun' to inherit the sample time - Configuring the subsystem 'test/vehicle' to inherit the sample time. I've added rate transitions before and after the submodel and also tried to make the system sample time greater or smaller than the sample time of the atomic subsystem, but received always the same error msg.

Appreciate for any ideas, suggestions etc.

Best Regards