Playback eventually ends wifh pixillation then crash

I have just started converting downloaded films & burning to DVD's using "convet x to dvd" program.
Unfortunately when I play back I find that despite the quality being excellent, after approximately 1 hour the picture starts to pixilate until it eventually crashes.
If I run the film through fully on fast forward, I do not encounter this problem and all appears perfect.

I am new to this, and to complicate matters I have just installed a new burner.

Any suggestions? How can I validate that the problem is not with the burner which appears ok in all other ways

Thanks

 

The media should be a known-to-be-good brand (Verbatim or Taiyo Yuden) burned at a moderate speed.

If the problem persists, let ConvertX do it's job - but burn the output files using Imgburn.

http://www.afterdawn.com/software/cdr_software/cdr_tools/imgburn.cfm

 

Thanks Attar, will see how I get on.