[R] Non-linear regression/Quantile regression

[despaired]

Hi,

I'm relatively new to R and need to do a quantile regression. Linear
quantile regression works, but for my data I need some quadratic function.
So I guess, I have to use a nonlinear quantile regression. I tried the
example on the help page for nlrq with my data and it worked. But the
example there was with a SSlogis model. Trying to write 

dat.nlrq <- nlrq(BM ~ I(Regen100^2), data=dat, tau=0.25, trace=TRUE)

or 

dat.nlrq <- nlrq(BM ~ poly(Regen100^2), data=dat, tau=0.25, trace=TRUE)

(I don't know the difference) both gave me the following error message:

error in getInitial.default(func, data, mCall = as.list(match.call(func,  : 
  no 'getInitial' method found for "function" objects

Looking in getInitial, it must have to do something with the starting
parameters or selfStart model. But I have no idea, what this is and how I
handle this problem. Can anyone please help?

Thanks a lot in advance!
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