Problems syncing from BuddyPress to WordPress

Hi All

Just added the User Sync plugin (latest version) on two sites that I want to keep synchronised.

Both sites run WP3.1.2 and the master site also runs BP1.2.8.

I've checked and double-checked all settings, but repeatedly get the following message when trying to perform a sync:
"There was a connection problem. Please check the URL and Key of the Master site."

Any known issues?