If it's 16x rated media, then I would try 12x or 8x instead of a 4x burn speed. Also, it's possible you ran across a bad blank (it happens). Your burner could be starting to go as well.
Additionally, read below:
from
Frequently Asked Questions (READ BEFORE YOU POST)
9. Why are my backups freezing, skipping, or showing a blocky pixellated mess during playback?
1. Update your burner's firmware (if available)
http://forum.slysoft.com/showpost.php?p=12794&postcount=10
2. Use good quality media (Memorex, Ritek, Princo, Fuji, TDK from Costco, and Maxell that are
not made in Japan are not good quality media).
Are you using inferior blank media? If you're not using Taiyo Yuden Premium, Verbatim, Maxell Plus, or Maxell Broadcast Quality, then chances are the answer is yes.
If you use poor quality blank media, then you should expect problems.
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3. Try lowering your burn speed a little (if you have a 16x burner and 16x rated media try writing to it at 12x or 8x instead of 16x)
4. If you're using +R, +RW, or +R DL media, change the booktype to "dvd-rom"
http://forum.slysoft.com/showthread.php?t=476 (step 3)
5. Avoid sticker labels (they tend to cause problems)
6. Try setting a custom size of 4300 in whatever burning program you're using (but if you're using good media, you shouldn't have to) if you're using regular single layer dvd-5 (4.7GB) discs.
7. Download
Nero cd-dvd speed. It's a free program. Select the tab labeled "scandisc". Insert the problematic backup disc, select the appropriate drive letter, and click "start". If Nero cd-dvd speed reports read errors, your backup is bad (which is the most likely case), your optical drive may be slowly dying, or your optical drive simply doesn't like the disc (or your choice of blank media)--even if the disc looks fine.
Bad burn quality is notorious around the end of discs (see step 6)
and also at layer breaks when using low quality DL media (use Verbatim +R DL media made in Singapore, and change the booktype to "dvd-rom")
