Thats interesting Bonnie, I've had the same thing happen to me with some USB's used with Mac. Even stranger I can read/write to it on a PC but then again not on the Mac.

Right clicking on your drive should give you the Get Info screen and show you the applicable permissions to your USB stick. You should see your username and Read & Write next to it. If something has changed, lord knows why, you might be able to reset your access by clicking the little padlock at the bottom of the window.

Re the other comments about reliability of USB drives, I agree. I have a hard drive or CD back up and then basically use the USB to carry things around on without having to sweat on losing the stick and something rrrrreally important…. but I guess you'd probably be aware of all that anyway so no need to labour the point :-)

Cheers,

Andrez