sapply error produced by grid search

Dear R User,

I'm trying to perform a grid-search for the ML estimator of the Box-Cox parameter for a linear mixed model. However using sapply to perform the grid search returns an error message. Here's a small example to demonstrate:

library(lme4)

# Function to fit model for a given lambda:
bc.fit <- function(lam,X,Z,Y){
              ybar <- exp(mean(log(Y)))
              if(lam==0){
                             w <- ybar*log(Y)
              } else {
                             w <- (Y^lam-1)/(lam*ybar^(lam-1))
}
bc.mod <- lmer(w~X+(1|Z))
as.numeric(logLik(bc.mod))
}

# Simulate data
x <- runif(1000)
z <- sample(1:100,1000,T)
b <- rnorm(100)[z]
y <- rnorm(1000,20+0.5*x+b,2)

# Perform search
lambda <- 1:10/10
sapply(lambda,bc.fit,X=x,Z=z,Y=y)

Produces the error:
Error in get(as.character(FUN), mode = "function", envir = envir) :
 object 'lambda' of mode 'function' was not found

However a single run works fine - bc.fit(lambda[1],x,z,y)

Other people appear to have had similar errors, caused by naming variables after existing functions, however I don't think that's the problem here. Any advice would be appreciated, thank you!