General Ducato Non Remote Cab Lock Problems

[shinetop]

Anyone advise me on problem with key not being able to turn lock on both doors. I can move the button up and down from INSIDE to activate the CL but no joy from outside the cab. My vehicle is a fiat ducato based 6M motorhome, any help appreciated,
shinetop

 

[Old-Boy racer]

Need more info, did it work before or have you just got it? If you've just got it then it probably means one of the locks has been changed and needs a different key. If it worked before, then the barrel or the key must be worn so needs replacing.