I'm moving the site from one server to another, but since DNS updates can take some time to propagate, I want to run the two in parallel for a while..

I've moved the entire site directory to the new server, and modified the config.php to point to the other server's mysql instance.

If I then update my hosts file to point at the new IP, the front index.php does the header/footer and nothing else (regardless of whether you're logged in or not). Seems lots of people have had this problem, but I haven't found a solution by searching the forums.

Anyway, here's where it gets strange. If I go the admin page for vBa and edit the modules (disable one and then re-enable it), it starts working from the new server, but stops working on the old one. If I go back to the old server and make the same edit, it reverts to the prior behavior.

I dumped the Mysql binlog to find out what was being updated, and all I see is two updates, one to adv_modules and the other to insert some serialized data into datastore. I don't see any part of this which would make it work with one web server, but not another.

Any suggestions? My next step in troubleshooting will be to compare the SQL statements from the two to find the specific differences, but I'm not confident that it will reveal anything useful, so I'm posting here in case anyone has a clue what's going on.