"NaNs produced" warning when trying to test the homogeneity (Levene's Test) with drc package

Question

Here is my problem. I've made many research online and I couldn't find a solution. I'm using the drc package to calculate ED50 for optical density.

LCEP : data LCEP structure

LCEP4 <- drm(DO~Conc, data=LCEP, fct=LL.4())
plot(LCEP4,type="all",col=3,lwd=2)

library(car) 
shapiro.test(residuals(LCEP4)) # Works ! 
leveneTest(residuals(LCEP4),as.factor(LCEP$Conc)) # Doesn't work 

Here's what i get ;

Levene's Test for Homogeneity of Variance (center = median)
      Df F value Pr(>F)
group  5     NaN    NaN
       0  

         

Same thing when trying to evaluate the adjustment quality

modelFit(LCEP4)

Here's what i get:

No test available

          ModelDf Log lik Df Chisq value p value
                                                
DRC model   

     

But, when i try the ANOVA test and the ED function, everything works.

I tried to multiplicate the DO factor (100 and 1000) ex; LCEP4 <- drm(DO*100~Conc, data=LCEP, fct=LL.4())

Didn't work.

I also ignored the problem, but I'm scared I'll be using the model even when the fit is wrong.

Hope you'll be able to help me ! Thank you :)