R help - Dec 2008 - NLS problem

Would appreciate some help on this problem please:

Using nls to solve for 5 parameters to a set of data, and for particular
mixes of the parameters the function can yield NaN and infinity returns.

Is is making nls fall over ­ I have tried starting values, lower and upper
bounds to no avail. New to R and not sure how to put constraints into this
function, the parameters have constraining relations.

Error messages I am getting with my tinkering are;

(1) Error in nlsModel(formula, mf, start, wts, upper) :
  singular gradient matrix at initial parameter estimates

(2) NaNs produced

Thanks, any help for a newbie would be great.

Glenn

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