upvc door, yale on side,era barrell?

hi all
i have lost a key for my door, and need to take the barrell out to change to lock. i have followed all the instuctions, and have changed one before for a friend. on my door it seems to be a different! when the retaining screw is removed, the barrell wont come out no matter what position i put the cam at. i have tried gently tapping with a hammer from both sides, moving the key round all the way, with the lock locked and open. it seems there is something else holding the lock in. i have removed the handle from both sides to make sure this is not catching it. the silver thin band than runs down the inside of the door says yale. the key is an era. i know this should be an easy repair, but for the life of me cant get the barrell out, please can someone help me out???
many thanks in advance ian f