User Sync is not working: Connection Error

Hello, I am having a problem using User Sync. When I try to enter the details and click Sync, I receive the following:

There was a connection problem. Please check the URL and Key of the Master site.

As far as I can tell, everything is correct, it just won't connect.

THIS IS NOT A MULTISITE!!! No multisite is installed ,these are two separate installs.

Any help here would be great,

Log file below:

Log file:

[2013-08-15 02:43:39][S] 01 - new subsite conection - central_url=http://community.tianjinbang.com;; replace_user=1;; overwrite_user=1;;***
[2013-08-15 02:43:39][S] 02 - sending request - url=http://community.tianjinbang.com/wp-admin/admin-ajax.php?action=user_sync_api;;***
[2013-08-15 02:43:39][S] 04 - sending request: something went wrong***
[2013-08-15 02:43:40][S] 0-10 - ajax actions***
[2013-08-15 02:43:40][S] 4-10 - hash sum error***
[2013-08-15 02:43:40][S] 3-10 - p or hash not set***
[2013-08-15 02:46:01][S] 01 - new subsite conection - central_url=http://community.tianjinbang.com;; replace_user=0;; overwrite_user=0;;***
[2013-08-15 02:46:01][S] 02 - sending request - url=http://community.tianjinbang.com/wp-admin/admin-ajax.php?action=user_sync_api;;***
[2013-08-15 02:46:01][S] 04 - sending request: something went wrong***
[2013-08-15 02:46:01][S] 0-10 - ajax actions***
[2013-08-15 02:46:01][S] 4-10 - hash sum error***
[2013-08-15 02:46:01][S] 3-10 - p or hash not set***

Print Screens of my configuration, to show there are no mistakes in the setup.

https://s3-ap-southeast-1.amazonaws.com/tianjinbang/WPMU/Master+Site.jpg

https://s3-ap-southeast-1.amazonaws.com/tianjinbang/WPMU/Sub+Site+(Before+Error).jpg

https://s3-ap-southeast-1.amazonaws.com/tianjinbang/WPMU/Sub+Site+(Error).jpg

Additional Information

Both wordpress installs are located on separate servers.

I am using the latest wordpress / buddypress installs. (Also the latest User Sync).

Server 1 is hosting just a regular Wordpress install
Server 2 is using wordpress + buddypress.

Again: NO MULTISITE!

Many thanks in advance for your help.