Hmm very strange now.....
I entered the following code
DoCmd.OpenReport "rptSupplyCover", acViewPreview, , "[CommencementDate] Between #01/04/03# And #30/04/03#"
And it displayed nothing so I changed the dates to
#01/04/2003# And #30/04/2003#
Now it filtered out the results after 30/04/03...