[BioC] normexp error

[Rani Elkon]

Hi,

I'm trying to normalize my data using limma's normexp method. The process 
fails at some chips giving the error message pasted below.
Does anyone know how this problem can be circumvented?

(I'm using limma 2.0.2 and R 2.1.1).

Thanks,
-Rani.

> dKa.RG.bgCorrect <- backgroundCorrect(dKa.RG, method="normexp", offset=50)
Corrected array 1
Corrected array 2
Corrected array 3
Corrected array 4
Corrected array 5
Error in optim(par = c(beta, log(sigma), log(alpha)), fn = normexp.m2loglik, 
:
        initial value in 'vmmin' is not finite