I am trying to get the promotors region using the following code but got an error.

query_ref <- ucscTableQuery(session, track="RefSeq Genes",table="refGene",
                        range=GRangesForUCSCGenome("mm9", "chr12"))

prom.refgene <- promoters(query_ref, upstream = 1000, downstream = 1000, use.names = FALSE)

Error in (function (classes, fdef, mtable) : unable to find an inherited method for function ‘promoters’ for signature ‘"UCSCTableQuery"’

This probably should have been labelled with rtracklayer rather than GRanges. The ucscTableQuery function creates an ucscTableQuery instance not a GRanges object to be able to use promoters directly. I think you have to use one of other helper functions listed in ?UCSCTableQuery first to convert it. Something like tracks or getTable