Bilbos way may work,but I think decrypting only removes the copy protection...
I would do this(it may sound a bit complicated,but it isn't):
1.Download and install a tool called AnyDVD...if its running any DVD copy protection will be ignored...really great tool...
2.Download and install a tool called IsoBuster...
3.Put the DVD that makes problems in your DVD drive and start IsoBuster...
Use IsoBuster to rip the DVD to your harddrive...Now if there is indeed something wrong IB will open a message window and tell you that some bits are fukked up and give you 3 options how to overwrite this(I can't remember all three options,but one was something with zeros(00) overwriting that didn't work for me)...
If the errors aren't to extensive...this should work...now you have the disc on your harddrive and can copy it to disc again...

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