I am trying to delete all the files on my DVD+RW disc

Help! I'm stumped by what looks like a very simple matter.

The problem is this: I am trying to delete all the files/folders on my DVD+RW disc. That's all. It shouldn't be hard, right? I have changed to a different disc & the same problem remains.

I've tried to launch Windows Explorer to manually delete the folder/files.
I get a message saying ''Error deleting file. Cannot delete VIDEO_TS. Files on this DVD drive are read only. You cannot copy or move files over to this DVD drive.''

Then, I've tried changing the folder properties to unhighlight the ''read only'' box but it won't save the setting. Also, the properties displays 2.3 Gb used and 0 bytes free. Weird, since the disc can hold 4.7GB.

I've also tried another way by clicking the ''Erase this CD-RW'' link at the upper left of Windows Explorer.
No matter what, I keep getting the same message: the CD writing wizard launches and bombs out with a ''Cannot complete the CD writing wizard. The wizard cannot complete erasing the disc...''message.

I'm stumped - pls. help!
AKan

P.S. Some extra detail in case it's helpful:
1) I am using an HP Pavilion a815n loaded desktop PC with an internal Lite-On DVDRW SOHW 1633S drive.

2) My ultimate aim is to burn to a DVD+RW disc a photo slideshow created in Pinnacle Studio 8.3.17. I am trying to overwrite the existing DVD+RW content with the new slideshow but it bombed out with a ''Incorrect disc media type. Pls. insert a correct media.'' This can't be correct though as I've already burned a prior Pinnacle Studio slideshow to the disc & simply want to burn a newer one to the disc. This is why I am trying to erase the disc!