if it is a 5V-only card, not only will it not work, it could damage your board! 
check out page 10 of the SAM460EX manual; it has a diagram there which shows you which cards will work and which will not. i hope it's both 3.3V and 5V compatible, and not 5V-only!
-- eliyahu
A 5V only card shouldn't fit into a 3.3V only slot if they used the right connector.
