Two things I can think of for you to check, others may have further suggestions:
Check the DVD you're trying to rip to see if it has any dirt or scratches.
It maybe that DVDDecrypter can't handle the copy protection by itself, since it is a bit long in the tooth to be used alone on pressed movie discs these days. You'll need something like AnyDVD to run alongside Decrypter in the background (to remove any copy protection), or a different program like DVDFab.
EDIT: I've also had the same error myself during the burning process, after I've ripped a disc; often it's been down to bad quality media, too fast a burn speed, or once again a dirty blank disc.