Whenever I am trying to burn a (data) DVD, I always receive several error messages, such as:

Interface Error: -50
The connection is not stable.

or

The drive reported an error:
Sense Key = ILLEGAL REQUEST
Sense Code = 0x30, 0x05
CANNOT WRITE MEDIUM - INCOMPATIBLE
FORMAT

and

Couldn't setup the track for writing.

My environment consists of:

* Apple PowerBook G4 Titanium (G4/400, 640MB RAM, 30GB HD) and
Cube (G4/450, 576MB RAM, 123 GB HD)
* MacOS X 10.2.6
* Freecom FX-50 DVD-/+R/RW CD-RW
* Emtec DVD-R 4,7GB single sided
* Roxio Toast Titanium 5.2.1
(-> Medium Info: DVD-R 4,4GB)

Any ideas?