A review of minpack.lm (1.1-4)

i need help with this package.

I have found it because I was searching for the Levenberg-Marquardt algorithm in R. I have apply the function nls.lm succesfully in some cases and it's wonderful. But now I have problems because of the function fn, some parameters cause errors (indetermination,divergence, non-finete values...) in the evaluation of my "fn". That's why I need to enter a bound to the parameters, not only the initial parameters with "par" but also a bound for them. Is it posible or do I need another function instead of nls.lm? And in this case, which one?

I will be really thank you for this. Thanks.