Windows 7 Backup Won't Burn DVD-R

New HP Laptop with Windows 7 - Windows Backup software doesn't recognise DVD as writeable, but Windows7 Explorer writes just fine to the same DVD-R.If I do Control Panel>System and security>Backup and Restore click on Backup Now ....this gives "Backup in progress..." bar - gets to about 25% and stops with the message "Insert Removeable media "Windows backup needs a CDDVD or USB drive to continue" (even though there is a DVD-R in E:, to which I have just successfully burned a very small test file using Explorer. E: shows on Backup pane as being selected as destination drive).If I click on "More information" another dialogue box pops up with instructions to "Label and insert a blank media"Please write the following label on a blank media and insert it into E:"FREDDY 02/01/2011"even though there is a labelled disc in there.(Of course that's a bum instruction from Windows anyway - it won't accept forward slashes - but that's OK - I label it without those. Still doesn't work.)If on the other hand I just select a file in Explorer and burn it ends up on the DVD no problem. With that same successfully burned DVD - Backup will still not recognise the DVD-R.I can use a DVD-R with a small test file burned OK to it, or a virgin disc from the box - makes no difference......