Pen Drive Problem

Hey guys, I have been having problems with my MBP and my pen drives. Whenever I delete things off my pen drive and try to put new files on, it says there is not enough room. There is nothing on the drive. I then look at the info and it says there is only a few MBs of space when it is empty (and they are multiple GB drives) Any ideas on how to fix this? Thanks!

The files are still on the drive until you delete them from your Trash Bin. To show this....if your pen drive is not attached and your dock shows an empty Trash Bin, connect the pen drive and see your trash magically fill up. There is a hidden folder created on the drive called "trashes" that will hold those files until the trash is emptied from the Trash Bin in your dock.

I am a new Mac user and I had to learn this as well!

Edit: If the trash bin does NOT show anything in it, then my answer is irrelevant and I don't know what the issue is. Sorry!