[R] Warnings in plot(model)

[Ronaldo Reis Jr.]

Hi all,
I try to make a residuals plot in a model, but the warnings occur.

> anova(m2)
Analysis of Deviance Table

Model: Negative Binomial(5.6937), link: log

Response: nind

Terms added sequentially (first to last)


                Df Deviance Resid. Df Resid. Dev P(>|Chi|)
NULL                               81    270.242
metros           1    0.005        80    270.237     0.943
habitat          7   92.843        73    177.395 3.222e-17
especie          1    6.843        72    170.552     0.009
metros:habitat   6   21.246        66    149.306     0.002
habitat:especie  7   50.657        59     98.649 1.073e-08
Warning message: 
tests made without re-estimating theta in: anova.negbin(m2)
> plot(m2)
Warning message:
NaNs produced in: sqrt(1 - hii)

What this warnings?

With envolopes function a error occur.
> envnbin(m2)
Error in solve.default(t(X) %*% W %*% X) :
        singular matrix `a' in solve

Thanks for all
Ronaldo
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