Testing an interaction with a random effect in lmer

I was hoping to get some advice regarding the testing of interactions,
when one factor is modelled as a
random effect...
I have a model with binomial error structure where the response 
variable is the proportion of time spent at
the main sett (animals were tracked for 28 consecutive days 
in each season, and were recorded either at the
main sett or an outlier sett, so the response variable is a number out of 28).
Animals from 9 social groups were tracked for 28 days in each of 
the four seasons of the year.
Thus, in my model, 'individual' nested within 'social group' 
are my random error terms.

model<-lmer(binom~season+(1|group/individual),binomial,data=data1)

Group explains some variation in the sett use patterns, 
and what i was wanting to test and display was an
interaction between season and group, as the raw data suggests 
that different groups may behave
differently in different seasons. Is there a way to do this in 
the lmer package?

When i put it in directly:

model<-lmer(binom~season*group+(1|group/individual),binomial,data=data1)

I get an error messgae:
Warning message:
In mer_finalize(ans) : gr cannot be computed at initial par (65)