Generate multiple samples

I'm trying to generate 500 samples of size 50 each, but it's not working. The program follows below.

require("gsl")

n=50
amostra = 500

alpha = 2
beta = 3

X=NULL
X<-matrix(0,nrow=n,ncol=amostra)

##### FUNCAO PARA GERAR UMA AMOSTRA

ree = function(n, alpha, beta){

u = runif(n, 0, 1)
x = -(alpha + beta * lambert_Wm1((-1 + u) * (alpha + beta) * exp(-                                                                                                                                                                                                                
(alpha + beta) / beta) / beta) + beta) / alpha / beta
return(x)

}  

##### FUNCAO DENSIDADE DE PROBABILIDADE

fx = function(x,t) { (t[1] ^ 2) * exp(-t[1] * x) * (1 + t[2] * x) / (t[1] + t[2]) }

##### FUNCAO LOG VEROSSIMILHANCA

 l = function(t) { log( prod(fx(dados,t)) )}

 lista_estimativas = NULL
 lista_sd = NULL
 obs = NULL

 repeat {

 dados = ree(n, alpha, beta)

 media = mean(dados)

 res = optim(c(1,1), fn=l, method="BFGS", control=list(fnscale = -1), hessian = TRUE)   #calcular o máximo da função

 estimate = res$par

 est = estimate[1]
 est2 = estimate[2]

 sd=sqrt(diag(solve(-res$hessian)))

 if( (!is.nan(sd[1]) & !is.nan(sd[2])) & (est >= 1/media & est <= 2/media) & est2 >0 ){

 lista_estimativas = c(lista_estimativas, res$par[1], res$par[2])
 lista_sd = c(lista_sd, sd)
 obs = c(obs,dados) 
  }

 if(length(obs) == n*amostra){ 
    break
   }
   }

While running the program, in addition to not generating the n * samples I need, it displays the following error:

Error in optim(c(1, 1), fn = l, method = "BFGS", control =  list(fnscale = -1),  : 
non-finite finite-difference value [1]
Além disso: There were 17 warnings (use warnings() to see them)

I do not know what else to do.