There have been some connection issues with Biomart. I am able to run your code chunk successfully using the development version
> library(biomaRt)
> ensembl = useMart("ENSEMBL_MART_ENSEMBL",dataset="hsapiens_gene_ensembl",
host = "oct2014.archive.ensembl.org")
> ensembl
Object of class 'Mart':
Using the ENSEMBL_MART_ENSEMBL BioMart database
Using the hsapiens_gene_ensembl dataset
> packageVersion("biomaRt")
[1] ‘2.45.5’
The most recent release version is now 2.44.4 where this problem has hopefully been fixed.