Hi, I am trying to use package cummeRbund to study differential gene expression in my sample groups of RNASEQ data On running the standard command :

cuff_data <- readCufflinks('WTCHG_diff_out2')
> mygene <- getGene(cuff_data, 'per')
I get below error 
No gene set returned (Gene might not be in database?)
Error in validObject(.Object) : invalid class "CuffGene" object: FALSE

Please suggest.