Ok you clever dicks!

I have a USB memory stick (4GB) that I keep MP3 files on...)

The USB memory stick has only used about one third of it's memory...

When I try to save files to it recently...it says "Directory cannot be found."

If I try to create a new file on this USB it says "Error 0x80070052 The directory or file cannot be created..

I can play the MP3 files already stored on this USB, but it wont let me save any more to it..

Is there any chance I can fix this USB stick? I have one of these stereo's in my car that will play MP3's from a USB memory stick...so I've been using this in my car of course and I suspect it's my car stereo that has damaged this USB...

Anyone else had this problem? Can it be easily fixed?

Thanks for your comments in advance!!