redoing website after 7 years

hi guys, I did php/mysql based website for one my client 7 years ago, in time when register_globals was on by default. hosting company upgraded server to php5/mysql5 and turned globals off. the site is doesn't work any more. I can define globals on again in .htaccess but rather not because it could be a big risk. to work again I have to spend a lot of hours to modify the code. boring job. but, I'm more concern does client has to pay the changes/upgrade or it's still "my obligation"? anybody had similar experience? thanks for any help. ll