[R] Singular Gradient

[This Wiederkehr]

I tried to fit data with the following function:

fit<-nls(y~ Is*(1-exp(-l*x))+Iph,start=list(Is=-2e-5,l=2.3,Iph=-0.3
),control=list(maxiter=500,minFactor=1/10000,tol=10e-05),trace=TRUE)
But I get only a singular Gradient warning...
the data can by found attached(there are two sampels of data col 1/2 and
3/4).

I tried to fix it by chanching the start parameters but that didn't solve
the problem.
Would it be a possibiliti to use the selfstart Model? How?

Thanks for any answers

This