in submitting a getBM(attributes) request to BioMart, i received this error message:

"Error in getBM(attributes = c("ensembltranscriptidversion", "ensemblgene_id", : The query to the BioMart webservice returned an invalid result: bioMart expected a character string of length 1. Please report this on the support site at http://support.bioconductor.org."

it has happened twice now so am reporting it. i in the same document, this worked fine the day previous. any assistance is greatly appreciated

This usually indicates some instability with the main Ensembl webserver. You can try querying one of the mirrors e.g.

mart <- useEnsembl(biomart = "ensembl", 
                   dataset = "dmelanogaster_gene_ensembl", 
                   mirror = "useast")

Values for the mirror argument are: useast, uswest, asia

I've updated the developmental version of biomaRt to try and detect this and do the redirection automatically in the future.