DVD movie occasionally Freezing

[nonicknamesleft]

I have a sony dru500a.Using record now dx- I copied a the tuxedo(backup) at 1 speed on bulkpaq media. Movie copied after about 1 hr with no error messages. When watching the film last night on a PS2 occasionally it was freezing/ getting stuck,then catching up. It is not something that stopped me watching the movie but was a bit annoying.
Has anybody experienced this before and do they know how to prevent this re-occuring?

Is it the media?
Is it the programme?

Any help appreciated.

Scott.