I won’t be able to help much, but I can tell you that as soon as someone who can help shows up, they will ask you to post the actual text of the error you’re getting as well as a runnable example that produces the error (one that generates simulated data and then tries to fit the model). They may even ask you to see if you can start with a simpler model (say one with only two groups).
I find that in the process of providing all that information, I’ve often had some insight into the problem.
Opher