I am following the user guide to estimate the dispersion of a dataset and got the following error messages:

> Patient <- factor(c(8,8,33,33,51,51))
> Tissue <- factor(c("N","T","N","T","N","T"))
> data.frame(Sample=colnames(y),Patient,Tissue)
  Sample Patient Tissue
1     8N       8      N
2     8T       8      T
3    33N      33      N
4    33T      33      T
5    51N      51      N
6    51T      51      T
> design <- model.matrix(~Patient+Tissue)
> rownames(design) <- colnames(y)
> design
    (Intercept) Patient33 Patient51 TissueT
8N            1         0         0       0
8T            1         0         0       1
33N           1         1         0       0
33T           1         1         0       1
51N           1         0         1       0
51T           1         0         1       1
attr(,"assign")
[1] 0 1 1 2
attr(,"contrasts")
attr(,"contrasts")$Patient
[1] "contr.treatment"

attr(,"contrasts")$Tissue
[1] "contr.treatment"

> y <- estimateDisp(y, design, robust=TRUE)
Error in locfitByCol(loglik, covariate, span = span, degree = 0) : 
  locfit required but is not available
> y$common.dispersion
NULL
> y <- estimateDisp(y, design, robust=FALSE)
Error in locfitByCol(loglik, covariate, span = span, degree = 0) : 
  locfit required but is not available
> plotBCV(y)
Error in plotBCV(y) : No dispersions to plot
>

Any suggestion to fix the error will be appreciated. 

The error message is telling you that you need to Install the locfit package. So do that and try your code again.

Thanks so much