New to R, please help :) error in table(group, resp) : all arguments must have the same length

[lecoote]

library("lordif")
Gender <- pre_op_knee$Gender
Resp <- pre_op_knee[paste("R", 1:5, sep = "")]
head(pre_op_knee)
GenderDIF <- lordif(Resp, Gender, criterion = "Chisqr", alpha = 0.01, minCell = 5)

the error is coming up after the last line of code... any help please?
I can share my excel sheet as well if that helps
Thanks,
Laura