nls problem with iterations

Hi,

I am using the nls function and it stops because the number of 
iterations exceeded 50, but i used the nls.control argument to allow for 
500 iterations. Do you have any idea why it's not working?

fm1 <- nls(npe ~ SSgompertz(npo, Asym, b2, b3), 
data=f,control=nls.control(maxiter=500))


Thanks for your help,
Cheers,
Karine.