problems duplicating for upgade

[r5mjh]

hi all, ive recently looked into upgrade our board from 3.7.1 to 4.2.3 i duplicated it on the dev site and and duplicate database, all works ok until i get to a certain stage of the upgrade and then it throws up a error while upgrading referring to the original site, is this because thats the url where the licence points?

no one can access except me as ive .htaccess etc, even if i try and upgrade on my offline server i get another error much earlier

i only want to do this incase of problems and would rather not mess up our board as theres 377,000 posts lol

any help appreciated as always thanx