User Sync - Synchronization Issue

Hey,

I recently purchased this plugin. To Sync my users from one site, to another site I set up recently. Both sites are on two different hosts. I tried the User Sync, and it syncs most of the users, however it comes up with a ' There was a connection problem. Please check the URL and Key of the Master site. ' after a couple of minutes.

Do you know what's making this happen? I tried the advice above, but no luck.

Cheers
Jake
Incept Network