Dvd to psp help?

i have a uk version psp, not the slim, model psp-1003k running firmware v3.73 and i cant get it to play dvd's. i can upload them ok but when it comes to playing them it starts to play and then i get a message that says this video cannot be played. i have tried using dvd fab,video9 and psp movie creator. music, pics go on fine and can be viewed but not the dvd's i upload. i have a 4g memory stick PRO duo installed and formatted using the psp format, is the firmware wrong for this model, i downloaded it using the network update and its the sony official, any help appreciated as it's doing my head in.