I am tryibng to use xval to run KNNB on an exprSet object. Trying to run down the source of my difficulties I went to the xval help file and executed the example shown below (also found in the xval help file). > library(golubEsets) > data(Golub_Merge) > smallG<-Golub_Merge[200:250,] > lk1<-xval(smallG, 'ALL.AML', knnB, xvalMethod='LOO', group=as.integer(0)) Error in xval(smallG, "ALL.AML", knnB, xvalMethod = "LOO", group = as.integer(0)) : no direct or inherited method for function 'xval' for this call I am running R Version 2.3.1, and the attached packages are Biobase 1.10.1, MLInterfaces 1.4.0, and golubEsets 1.2.4. Following advice given for other instances of this error call I reinstalled the Biobase package using biocLite and ran the update.packages() function and replaced all the packages listed. I am new to R and any help would be appreciated. Thanks, Mike