Silver ps2 Question

[OURKID]

I have a 'silver' ps2 and am having it chipped using a dms3 chip ... i already have my other done and works a treat.
Now here lies the problem...when the chip is fitted the ps2 will play multi-region dvd's but will not play 'back-up' games.
It will play originals ok ...i have had tried quite a few different chips in it messiah and the such but all with the same result.
Any ideas??
The silver is a 50000 version and is only a few months old so i don't know whether sony have made modifications to the newer models to try to prevent chipping??
Any info will be much obliged