cosinoRmixedeffect: an R package for mixed-effects cosinor models

Question

[Agnia]

I am running the interaction model between two variables (compound and agonist):

fit.cosinor.mixed(y="value", interaction=c("compound","agonist"), random="1+rrr+sss|sample_id", data=du.model)

For the sample id, I have 24 observations each in triplicate (72 in total). And I have 2 compounds and 2 agonists. However I keep getting an error:

Error: number of observations (=72) <= number of random effects (=72) for term (1 + rrr + sss | sample_id); the random-effects parameters and the residual variance (or scale parameter) are probably unidentifiable