When I copied in your model code I noticed immediately a basic syntax issue; in that you need to close brackets; if you look at the general tab you would have seen the errors noted in red too.
I haven't looked much furhter into you code but I did notice that there is some issue with the code/data still as you get this error in Warnings and errors when I try to execute.
Observable 'PID_score' category probabilities not descending
As I have to go into a meeting for the rest of the day I attach my project(v6.4) so far, you may need to confirm the mappings etc. and of course some initial estimates too.
Simon
PS Note this also being dealt with as Certara Support Case #00163890
Oh yes! I missed the bracket while quoting the model text here in the forum, when I looked back I saw the 2nd bracket was there in NLME.
So, bracket could not be an issue.
I tried with initial estimates of coefficients, with larger the probability, lower the coefficients but still it didn't work.
Can "Observable 'PID_score' category probabilities not descending" could be a problem?
But how? because with disease progression there's neither absolute pain reduction nor absolute worsening with time.
Regards
Arindam