Hi,
not sure what it is, but there seems to be a difference when using Partition Mini tool and the ext3/ext4 partitions used by the phone..... Never could get any sd-card partitioned with the Mini Tool work with my Prevail.
Best is to use Clockworkmod to partition and then ( if needed ) use Kouma's SDParter to make other partitions on your card, all directly on the phone !
SDParter :
http://db.tt/CFKodPp7