I want to use a R script (the beginning below) to calculate ELISA results. My ELISA kit has 5 standards, and sample result is (the first standard is 'zero' but it need to be changed into non-0)

OD conc 1.16544997692108 0.000001 0.861099988222122 0.25 0.54805001616478 1 0.344400003552437 4 0.112999998033047 16

library("drc")
#####ELISA TEST
rm(list=ls())
library (drc)
###copy data for standards from excel (header – OD, conc) in windows use paste function
stdcrvdata <- read.table(pipe("pbpaste"), sep="\t", header=T) 
stdcrvdata$logconc <-log10(stdcrvdata$conc)# log10 from conc
plot(stdcrvdata$logconc, stdcrvdata$OD, main="log standard curve", xlab="x=log(conc)", ylab="y=OD")
fit<-drm(formula =   OD ~ logconc , data = stdcrvdata, fct = LL.4())

the last line of the script (fitting) results with error

Error in optim(startVec, opfct, hessian = TRUE, method = optMethod, control = list(maxit = maxIt, : initial value in 'vmmin' is not finite Error in drmOpt(opfct, opdfct1, startVecSc, optMethod, constrained, warnVal, : Convergence failed

how to fix that? The script works when used for 9-standard set.