Try this:
Select the drive and go to File>Get Info.
Under the triangle for Ownership & Permissions make sure that Read & Write is selected from the pulldown menu beside Others.
Now, this makes that drive wide-open to anyone that logs into the computer. As well, you may want to make sure that No Access is not selected in any of the access fields.
If I'm correct, what's happened is that you need to make the drive shareable in addition to turning on file sharing.