cannot rewrite dvd rw

[Jan Brosius]

Hi,

I have installed fedora 7 (64 bit). I installed k3b. The first time I 
can write a file successfully to a dvd RW disc. But afterwards when I 
try to add a file to this dvd disc it fails giving me the following 
error messages

- :-(/dev/sdc0: unable to proceed with recording: unable to unmount
- Fatal error at startup: Device or resource busy
- unable to eject media

But before these error I get the following messages:
- Waiting for media
- Writing DVD-RW in incremental mode.
- Unmounting disk
- Searching previous session
 - Using growsisofs 7.0 - Copyright (C) Andy Polyakov ..
- Unmounting medium
- Starting disc write ...

Also when I try to use CD/DVD Creator I get the following error message: 
There was an error writing to the disc: The target DVD drive is still in 
use.
Can someone tell me what to do?

Thanks for any help
Jan