I need help in estimates lme models

Question

I'm analyzing two models of class LME for longitudinal data (observations in two times), but this message appears Error in lme.formula(y ~ x, random = ~1 | id, data = data_long) : nlminb problem, convergence error code = 1 message = false convergence (8). This error appears on two models, what is it?

My outcome is continuous and normal errors. Can I use another estimator or some argument to correct this error? My predictor in dichotomous.

Output R:

mod7 <- lme(y~x,random=~1|id, data=data_long)
# output:
# Error in lme.formula(y ~ x, random = ~1 | id, data = data_long) :
# nlminb problem, convergence error code = 1 message = false convergence (8)

summary(mod7) 
# output:
# Error in lme.formula(y ~ x, random = ~1 | id, data = data_long) :
# nlminb problem, convergence error code = 1 message = false convergence (8) 
# Error in h(simpleError(msg, call)) : erro na avaliação do argumento 'object' na seleção do método para a função
# 'summary': 'objeto 'mod7' não encontrado'

I need estimates a lme model for hormone by sleep duration (short X normal), but the model no converge.