Error with ls.mixed and weights

library(Zelig)
set.seed(1000)

x <- runif(1000, -1, 1)
y <- x + rnorm(1000)
wt <- rexp(1000)
id <- rep(1:20, times = 50)
d <- as.data.frame(cbind(y, x, wt, id))

m1 <- zelig(y ~ x + tag(1|id), model = "ls.mixed", weights = "wt", data = d)
m2 <- lmer(y ~ x + (1|id), weights = wt, data = d)