So, I just ran into this same issue today and was able to resolve it just by clearing out my workspace, closing, then reopening the file.
In my specific case, I had defined a variable named size and had given it as an array. This caused Simulink to become confused because that Repeating Sequence Stair block uses a function named size.
For whatever reason, this Simulink block was pulling from the base workspace my own variable and trying to interpret it has a function. This was extremely frustrating. I can't think of any other platform that would not have their own internal variables/functions scoped outside of the global base workspace. Why anyone would design a software platform like this is beyond my comprehension.
