Hi,
The lmer() function seems to work well for a mixed model having a random effect with only one level: it doesn't crash and there's not even a warning. I'm not a specialist about the numerical mathematics behind lmer(), but isn't it possible to see somewhere in the output there's a problem such as a convergence problem for instance ? (in such a situation SAS 9.2 returns a "note" about a problem with some Hessian matrix).
Stéphane
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