As the title says even when the correct password is entered sudo rejects it. I have been to the sudo website and had a look at the faq and sure enough the question has been asked. The answer is that the 'config.h' maybe missing a definition. Now here is the problem, I don't have a 'config.h' for sudo. The only config.h's are for my own c programs. Anybody able to help this gray haired old fogey out please?
Thank You in advance.

Are you sure that /etc/sudoers has been configured correctly? Is your user listed in here? Did you grant all actions, or just some? If not, this could explain why.

Thank you Ian. The dope that I am I misinterpreted what I was supposed to do. I just had the brainwave of adding my normal login name to the sudoers file and lo and behold it now works. What I was doing was entering my root password. I did try my normal login password but got a very curt reply that I was to be reported to the authorities. Thank you for the reply and you were correct,.
Sorted.

Nice one