Picture problems with most but not all vcd's - help

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I have recently bought a Sony dvp ns-305 and have used it sucessfully to play dvd's, mp3's and cd's but I am having problems with vcds.
I bought four vcds from the same person and they are all the same make and colour, however three out of the four will not play without interference. The interference is very much like that a video recorder has when it requires tracking. Any suggestions. Thanks

[roar]

Sorry, forgot to say that I can play all four of these vcds on my computer