R help - Sep 2008 - New member with question on multiple comparisons in mixed effects models

Dear fellow R.users/.lovers,
 
I am very new to both R and this list, so I hope you will be patient with me in
the beginning if my enquiries are inappropriate/unclear.
 
I am trying to perform some rather complex statistical modelling using
mixed-effects models.
 
I have, after a rather difficult beginning, finally boiled down my model (using
the lme function in nlme) to a couple of fixed effects and their interactions,
plus a couple of nested random effects.
 
For the moment I will not include the details because the dataset is rather
large and without it is difficult to be more specific, but I can provide them if
requested.
 
My question is maybe a bit trivial, but I would like to get out of the model the
pairwise comparisons for all the factor levels using TukeyHSD, but when I try to
do this using the "glht" method in the multcomp library I get an error
message which seems to indicate a wrong synthax, yet I think I am following the
instructions given on the package documentation. Below are the code lines and
the R reply.
 
> glht(inner.exch.M9.lme,linfct=mcp(Personality:Day = "Tukey"))
Error: unexpected '=' in
"glht(inner.exch.M9.lme,linfct=mcp(Personality:Day ="

(inner.exch.M9.lme is the model object, Personality and Day are the two fixed
factors the levels of which I want to compare)
 
I also tried without the interaction symbol and only one factor, with the same
result.
 
As I understand it, the multcomp package is new so maybe the method is not
implemented for complex designs yet.
 
Any suggestion will be appreciated (including such as "read the
instructions" if they can point me to such instructions!).
 
 
Thank you very much in advance and all the best
 
Giuliano