R help - Sep 2011 - nls, the four parameter logisitc equation, and prediction band

I have uploaded a datafile that contains the following two variables: time
(X value) and response (Y value).  This is a fairly extensive file (with >
16000 entries).  I have two questions:

1. I want to use the following equation to regress Y on X: Y-hat = min +
(max-min)/(1 + (X/EC50)^Hillslope).

Here is my R command:

nlsout <- nls(Y ~ (0 - (100-0)/(1 + (X/EC50)^hill)), start=c(EC50=125,
hill=-1))

However, I get the following error message:

Error in numericDeriv(form[[3L]], names(ind), env) :
  Missing value or an infinity produced when evaluating the model
Could someone explain the error message to me, please, and what I need to do
to be able to run the command without error?  The problem is that this exact
same formula works on the exact same dataset when I use a macro in Excel
(unfortunately I don't have the code, though).


2. I want to compute the prediction band for the above regression.

Any help will be greatly appreciated.

Thanks,

Joe

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