[BioC] Error: expresso

[S Peri]

Hello group, 

 I am trying to normalize using expresso module and I
am getting the following error. In fact I followed the
example given at the bottom of help file.  The
following is what I get: 
> abcel.data.norm = expresso(abcel.data,
bgcorrect.method = "rma", normalize.method =
"constant", pmcorrect.method = "pmonly",
summary.method = "avgdiff")
background correction: rma 
normalization: constant 
PM/MM correction : pmonly 
expression values: avgdiff 
background correcting...Error in bg.correct(afbatch,
method = bgcorrect.method) : 
        No direct or inherited method for function
"bg.correct" for this call


Any suggestions where it is going wrong. 
Thank you. 

SP