? Subscript indices must either be real positive integers

Dear all,
I have just tried to conduct a simulation of a deterministic model and received the above message from Matlab, after it returned the steady state values of the model (which were all correct). The model is linear and all variables are expressed in deviations from the steady state. I have used the command “linear” but this does not seem to be responsible for the problem as the problem persists when I delete it. I have attached the mod file. Many thanks for your help!
nonstochlinear.mod (1.87 KB)