The command has indeed failed with message:
Abstracting over the terms "S", "p" and "u" leads to a term
fun (S0 : Type) (p0 : proc S0) (_ : S0) => p0 = Tick -> True
which is ill-typed.
Reason is: Illegal application: 
The term "@eq" of type "forall A : Type, A -> A -> Prop"
cannot be applied to the terms
 "proc S0" : "Prop"
 "p0" : "proc S0"
 "Tick" : "proc unit"
The 3rd term has type "proc unit" which should be coercible to 
"proc S0".