I am trying to use one of the variance function classes (e.g., varClasses -varConstPower or varPower) When I run the model under default conditions or specify varIdent explicitly I do not have any problems. If I try to use anything else I get error messages of the form "Error in na.fail.default(list(USUBJID = c(1636L, 1636L, 1636L, 1636L, : missing values in object" I have simplified my data to the bare minimum, I am positive there are no missing records, and my initial parameter estimates are in a range where the model happily converges otherwise. I am a bit unsure as to what is going on. Does anyone have anything to suggest for diagnosing this problem? Thanks -- View this message in context: http://www.nabble.com/NLME-tp25405582p25405582.html Sent from the R help mailing list archive at Nabble.com.