When you want to move a Drupal site from one hosting server to another you have to ensure that the site works the same way on the new server as it used to work on the old server. There is no real fool proof way of doing this other than to meticulously document all the custom aspects associated with setting up the site and verifying it on the new server. The following is a checklist of information you have to collect before you move your Drupal site from one server to another.
Checklist: Migrate from one server to another