Connection error after moving to a new server

Both sites are running latest WP and latest User Sync. Both sites are on same server, the sub-site is a subdomain.

Migrated the site over to our new server, and since then users are not syncing. I've disconnected the sites, uninstalled the options, and attempted to connect them again. But I just get this error: "There was a connection problem. Please check the URL and Key of the Master site."

This is the error log from the sub-site:

[2013-11-28 23:08:37][S] 01 - new subsite conection - central_url=http://*Moderated on request*;; replace_user=0;; overwrite_user=0;;***
[2013-11-28 23:08:37][S] 02 - sending request - url=http://*Moderated on request*/wp-admin/admin-ajax.php?action=user_sync_api;;***
[2013-11-28 23:08:37][S] 03 - sending request - response=0;;***

No error log on the main site.

Any ideas?