Error message with lme

Dear All,

I tried to run an R scipt on a set of data with lmList function and it worked fine, but as i tried to run with lme function, the program suddently give a message error. Both script and message error are? shown below

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dp <- rep(rev(1:11), 261)
sub1 <- data.frame(sub1, dp, or)
tmp <- groupedData(Temp ~ dp? | or, data = sub1, FUN = mean, order.groups = TRUE, labels = list(x = "Depth", y = ??? ??? 

??? "Temperature"),? units = list(y = "(0C)"))

lm.lis1 <- lmList(tmp)
lm.lme1 <- lme(lm.lis1)

Error in lme.formula(fixed = Temp ~ dp, data = tmp, random = list(or = c(2.45530618001172,? : 
? nlminb problem, convergence error code = 1
? message = iteration limit reached without convergence (9)
#################################################################################

Could?someone advice me the?way to tackle on this problem?

Thank you
Fir