Thanks Ruben. Your suggestion about more deeper analysis about the model itself is really helpful. I am trying out some new initial values based on the analysis of the special T2 in the model. -- View this message in context: http://r.789695.n4.nabble.com/nls-problem-with-R-tp3494454p3495663.html Sent from the R help mailing list archive at Nabble.com.