[R] Problems with glht function for lme object

[anord]

Dear all, 

I'm trying to make multiple comparisons for an lme-object. The data is for
an experiment on parental work load in birds, in which adults at different
sites were induced to work at one of three levels ('treat'; H, M, L). The
response is 'feedings', which is a quantitative measure of nest provisioning
per parent per chick per hour. Site is included as a random effect (one
male/female pair per site). 

My final model takes the following form:
feedings ~ treat + year + data^2, random = ~1|site,data=feed.df

For this model, I would like to do multiple comparisons on 'treat', using
the multcomp package:
summary(glht(m4.feed,linfct=mcp(treat="Tukey")))

However, this does not work, and I get the below error message.

Error in if (is.null(pkg) | pkg == "nlme") terms(formula(x)) else slot(x,  : 
  argument is of length zero
Error in factor_contrasts(model) : 
  no ‘model.matrix’ method for ‘model’ found!
 
I suspect this might have quite a straightforward solution, but I'm stuck at
this point.
Any help would be most appreciated. Sample data below.

Kind regards, 
Andreas Nord
Sweden

==============
feedings     sex site  treat year  date^2
1.8877888   M  838     H 2009      81
1.9102787   M  247     H 2009      81
1.4647229   M  674     H 2010      121
1.4160590   M 7009     M 2009      144
1.3106749   M  863     M 2010      196
1.2718121   M   61     M 2009      225
1.2799263   M  729     L 2009      256
1.5829564   M  629     L 2009      256
1.4847251   M  299     L 2010      324
1.2463151   M  569     L 2010      324
2.1694169   F  838     H 2009      81
1.5966899   F  247     H 2009      81
2.4136983   F  674     H 2010      121
1.7784873   F 7009     M 2009      144
1.6681317   F  863     M 2010      196
2.3691275   F   61     M 2009      225
2.0672192   F  729     L 2009      256
1.6389902   F  629     L 2009      256
0.9307536   F  299     L 2010      324
1.6786767   F  569     L 2010      324
==============


-- 
View this message in context: http://r.789695.n4.nabble.com/Problems-with-glht-function-for-lme-object-tp3179128p3179128.html
Sent from the R help mailing list archive at Nabble.com.