groupedData Error Using outer=TRUE

I'm using groupedData from nlme. I set up a groupedData data.frame with
outer=~group1. When I try to plot with outer=TRUE, I get "subscript out
of bounds." This happens most of the time. When it works, I get
spaghetti-type plots for comparing groups. But I don't understand why it
doesn't usually work.

longa.mod.1.gd <- groupedData(mod1.logit~time|

name/eye,outer=~group1,data=longa.mod.1)

plot(longa.mod.1.gd)
plot(longa.mod.1.gd,outer=TRUE)

Error in attribs[["outer"]][[displayLevel]] :
        subscript out of bounds

What am I doing wrong?