Suddenly getting errors whenever copying contents of DVD-Rs to desktop

[copyerror]

I take a lot of pictures and a significant portion of my workflow for processing them involves loading them onto my laptop, organizing them into folders, burning them onto a blank DVD as a back up and then transferring them to my main computer (which I do all my editing on) via the DVD. I've been doing this for the past 5+ with no problems up until now. Starting a day or two ago I can't seem to copy the contents of any of my burned DVD-Rs to my computer without getting one of these two error messages:

Error Copying File or Folder
Cannot copy (filename): The request could not be performed because of an I/O device error.

-or-

Error Copying File or Folder
Cannot copy (filename): The volume for a file has been externally altered so that the opened file is no longer valid.

The copying process goes smoothly for the first 2 or so gigs (out of ~4) and the disc spinning can be heard but then it goes silent and the copying goes much slower, eventually stopping entirely and giving me one of those errors. I googled both error messages but couldn't find much that applied to my situation (copying files from dvd-rs to a desktop) and I'm not sure what they mean or what to do about them. Any help would be much appreciated!

(Btw, OS is Windows XP Pro SP 2)

 

[JMMD]

Either the discs/burns are bad or your DVD drive laser is having issues reading the discs. I would suggest trying a different optical drive and see if you have the same issues.