Problem with access to 3 folders on my external drive

Hi im having a problem, i have a macbook pro and a external drive iomega for mac, im a dj so i have all my music on my external hard drive so i created folders to organize my music, so suddenly i was gonna put some songs on a folder that i've created, and i realize that it's empty and i don't have permision to access, rename the folders also erase them, i've checked the sharing & permissions box, and the only thing that appears is "you have unknown access" even the padlock doesn't appear, well if someone can help i would be really appreciate. thanks!