Hi, eset is an expressionset based on hgu133plus2 platform. Using hgu133plus2.db package, I want to map probes to UniGene cluster IDs. It results in an error message.>xx=hgu133plus2UNIGENE >uniaf1=xx[[as.character(featureNames(eset))]]Error in .checkKeys(value, Lkeys(x), x@ifnotfound) : value for "AFFX-r2-Hs18SrRNA-3_s_at" not found Could you please help me figure out what creates the error ? Many thanks Vickie [[alternative HTML version deleted]]