Using influence.lme (cars package) with cooks.distance function with lme model from nlme in R

Question

I have currently built an mlm using the lme package in R. I am trying to get a measure of cook's distance from this model. I am using the influence function from the cars package, which the documentation says you can read into the cooks.distance function. However, when I put the result of this function in the cooks.distance function, it returns values ranging from 4.27 to 1609.96.

acc_2_d_l2b <- lme(Acc~load1+load2+PSWQd_Acc_C_p58, random=~1|Subject,
                   weights=varIdent(form=~1|trial), data=final_data_long_p58,
                   method="REML", na.action="na.exclude")

b <- influence(acc_2_d_l2b, group=c("Subject"), obs=TRUE)

a <- cooks.distance(b, group=c("Subject"))