[R] mixed model

[NATALIA F TCHETCHERINA]

 Hello all,
 I have problem with setting up random effects.
 I have a model:
 y=x1+x2+x1*x2+z1+z1*x2
 where x1, x2, x1*x2 are fixed effects
 and z1, z1*x2 are random effects (crossed effects)
 I use library(nlme) 'lme' function.
 My question is: how I should set up random effects?
 I did 
 lme(y~x1+x2+x1:x2, data=DATA, random=~z1+z1:x2, na.action='na.omit')
 but it did not work.

 Sincerely, Natalia.