I have some problem with my lienar mixed model.

When I do my model with the maximum likelihood, I have no error. But, when I want the confidence intervals, I get the Error : " cannot get confidence intervals on var-cov components : Non positive definite approximate variance-covariance".

Does that mean my model isn't ok ?

Plus, when I do the same model with "REML", the error is not here anymore. But the AIC is less good and I can't do anova test anymore too ...

What can I do ?

Thanks for your help,


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