[BioC] xval

[mpg33 at drexel.edu]

I am attempting to use the xval function to run knnB on an exprSet object.  The command line given by the help file doesnt seem to work.  When I run 
lk1<- xval(smallG, 'ALL.AML', knnB, xvalMethod='LOO', group=as.integer(0))

I get the error Error in xval(smallG, "ALL.AML", knnB, xvalMethod = "LOO", group = as.integer(0)) : 
        no direct or inherited method for function 'xval' for this call

Any idea what the problem could be?