Exactly what rule has been broken when lme (package nlme) produces the error message "Incompatible formulas for groups in random and correlation"? Here is what I am trying to do: lme(Y ~ trait-1, random = ~trait-1|sire, corr = corSymm(form = ~trait|cow)) Trait, sire and cow are factors (cow nested within sires). I want to estimate a (genetic) covariance matrix at the sire level, plus a residual covariance matrix, both matrices t x t, where t is the number of levels in trait. =====================================I.White ICAPB, University of Edinburgh Ashworth Laboratories, West Mains Road Edinburgh EH9 3JT Fax: 0131 650 6564 Tel: 0131 650 5490 E-mail: iwhite at staffmail.ed.ac.uk