Synchronize users to contacts gives non-recoverable error in Demo 1.7

I tried synchronize users to contacts on the 1.7 demo site and received the following non-recoverable error:
Synchronize Users-to-Contacts

unrecoverable error
Sorry. A non-recoverable error has occurred.

Return to CiviCRM menu.

Error Details:
Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -5
[message] => DB Error: already exists
[mode] => 16
[debug_info] => INSERT INTO civicrm_uf_match (uf_id , contact_id , domain_id , email ) VALUES ( 3 , 102 , 1 , 'dggreenberg@gmail.com' ) [nativecode=1062 ** Duplicate entry '102' for key 3]
[type] => DB_Error
[user_info] => INSERT INTO civicrm_uf_match (uf_id , contact_id , domain_id , email ) VALUES ( 3 , 102 , 1 , 'dggreenberg@gmail.com' ) [nativecode=1062 ** Duplicate entry '102' for key 3]
[to_string] => [db_error: message="DB Error: already exists" code=-5 mode=callback callback=CRM_Core_Error::handle prefix="" info="INSERT INTO civicrm_uf_match (uf_id , contact_id , domain_id , email ) VALUES ( 3 , 102 , 1 , 'dggreenberg@gmail.com' ) [nativecode=1062 ** Duplicate entry '102' for key 3]"]
)