Problem with simulation

Dear:

I am having problem with simulation. Sometimes for 100 iteration, my
program works but sometimes give error message regarding some "built-in
function" which I never used
in my code. I have no idea about the problem. Any suggestion, comments or
idea regarding this would be highly appreciable. Thanks.

I have used ---- "maxLik()" and "BBsolve()" in my code. Error message shows
regarding "optim()".

Well you may have not used "optim" explicitly but what about maxLik?
If you had read the help for maxLik you would have seen that there is a link to optim, which within the context of maxLik would seem to imply that the maxLik uses optim.

You don't even provide the exact error message.
Without any reproducible code it is not possible to give any kind of suggestion, comment or idea except: please provide code that exhibits the issue.

Berend