[R] weird (?) resid(.) from 2-level lme()

[Irene Mantzouni]

Hi all!
 
I am trying to fit a 2-level hierarchical lme(). 
I can extract ranef() and coef() without problems for levels=1:2. 
However, when it comes to resid() at level=2, the resulting list has some unnamed entries (label="NA"). I checked with my data (NAs have been omitted) and I found out that it gives 2-3 residuals less in each subgroup. 
Any ideas what might be wrong? 
 
Thank you!
 
Irene