CiviCRM non-recoverable error when completing donation with email address used before

After using the same email address I used before, I clicked on Confirm on the confirmation page and then saw:

Sorry. A non-recoverable error has occurred.

DB Error: already exists

Database Error Code: Duplicate entry 'tjcook@gmail.com-1' for key 4, 1062

Return to home page.

Error Details:

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

[code] => -5
[message] => DB Error: already exists
[mode] => 16
[debug_info] => UPDATE civicrm_uf_match SET uf_id = 10 , uf_name = 'tjcook@gmail.com' , contact_id = 515 , domain_id = 1 WHERE ( civicrm_uf_match.id = 10 ) [nativecode=1062 ** Duplicate entry 'tjcook@gmail.com-1' for key 4]
[type] => DB_Error
[user_info] => UPDATE civicrm_uf_match SET uf_id = 10 , uf_name = 'tjcook@gmail.com' , contact_id = 515 , domain_id = 1 WHERE ( civicrm_uf_match.id = 10 ) [nativecode=1062 ** Duplicate entry 'tjcook@gmail.com-1' for key 4]
[to_string] => [db_error: message="DB Error: already exists" code=-5 mode=callback callback=CRM_Core_Error::handle prefix="" info="UPDATE civicrm_uf_match SET uf_id = 10 , uf_name = 'tjcook@gmail.com' , contact_id = 515 , domain_id = 1 WHERE ( civicrm_uf_match.id = 10 ) [nativecode=1062 ** Duplicate entry 'tjcook@gmail.com-1' for key 4]"]
)

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