SUMMARY: I am using CiviCRM 4.6.2 on WordPress 4.2.1 for a membership sign and renewal site and keep hitting this wall on this DB Error: already exists related to user registration on a membership contribution page.
It's worth noting that this is a relatively fresh install with no contacts (besides the administrative account and the membership organization contact), authorize.net set up and some custom fields added via a custom profile (the profile forces user registration).
Here is the log and backtrace: (email removed..)
May 06 15:28:46 [info] $Fatal 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 (domain_id , uf_id , uf_name , contact_id ) VALUES ( 1 , 2 , 'email@example.com' , 4 ) [nativecode=1062 ** Duplicate entry 'email@example.com-1' for key 'UI_uf_name_domain_id']
[type] => DB_Error
[user_info] => INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALUES ( 1 , 2 , 'email@example.com' , 4 ) [nativecode=1062 ** Duplicate entry 'email@example.com-1' for key 'UI_uf_name_domain_id']
[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 (domain_id , uf_id , uf_name , contact_id ) VALUES ( 1 , 2 , 'email@example.com' , 4 ) [nativecode=1062 ** Duplicate entry 'email@example.com-1' for key 'UI_uf_name_domain_id']"]
)
May 06 15:28:46 [info] $backTrace = #0 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Error.php(235): CRM_Core_Error::backtrace("backTrace", TRUE)
#1 [internal function](): CRM_Core_Error::handle(Object(DB_Error))
#2 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/PEAR.php(931): call_user_func((Array:2), Object(DB_Error))
#3 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/DB.php(976): PEAR_Error->PEAR_Error("DB Error: already exists", -5, 16, (Array:2), "INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALU...")
#4 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/PEAR.php(564): DB_Error->DB_Error(-5, 16, (Array:2), "INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALU...")
#5 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/DB/common.php(1905): PEAR->raiseError(NULL, -5, NULL, NULL, "INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALU...", "DB_Error", TRUE)
#6 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/DB/mysql.php(899): DB_common->raiseError(-5, NULL, NULL, NULL, "1062 ** Duplicate entry 'email@example.com-1' for key 'UI_uf_name_domain_id'")
#7 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/DB/mysql.php(328): DB_mysql->mysqlRaiseError()
#8 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/DB/common.php(1216): DB_mysql->simpleQuery("INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALU...")
#9 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/DB/DataObject.php(2442): DB_common->query("INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALU...")
#10 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/DB/DataObject.php(1060): DB_DataObject->_query("INSERT INTO civicrm_uf_match (domain_id , uf_id , uf_name , contact_id ) VALU...")
#11 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/DAO.php(450): DB_DataObject->insert()
#12 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/BAO/UFMatch.php(56): CRM_Core_DAO->save()
#13 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/BAO/CMSUser.php(247): CRM_Core_BAO_UFMatch::create((Array:3))
#14 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Contribute/BAO/Contribution/Utils.php(478): CRM_Core_BAO_CMSUser::create((Array:53), "email-5")
#15 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Contribute/Form/Contribution/Confirm.php(1526): CRM_Contribute_BAO_Contribution_Utils::createCMSUser((Array:53), "4", "email-5")
#16 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Contribute/BAO/Contribution/Utils.php(120): CRM_Contribute_Form_Contribution_Confirm::processContribution(Object(CRM_Contribute_Form_Contribution_Confirm), (Array:53), NULL, "4", Object(CRM_Financial_DAO_FinancialType), TRUE, TRUE, FALSE, (Array:1))
#17 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Member/BAO/Membership.php(1338): CRM_Contribute_BAO_Contribution_Utils::processConfirm(Object(CRM_Contribute_Form_Contribution_Confirm), (Array:53), (Array:33), "4", "2", "membership", (Array:0), FALSE, TRUE)
#18 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Contribute/Form/Contribution/Confirm.php(1903): CRM_Member_BAO_Membership::postProcessMembership((Array:47), "4", Object(CRM_Contribute_Form_Contribution_Confirm), (Array:33), (Array:0), (Array:0), (Array:11), (Array:1), TRUE, NULL, FALSE, "2", (Array:0), TRUE)
#19 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Contribute/Form/Contribution/Confirm.php(1019): CRM_Contribute_Form_Contribution_Confirm->processMembership((Array:47), "4", (Array:0), (Array:0), (Array:33), (Array:0), TRUE)
#20 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Form.php(345): CRM_Contribute_Form_Contribution_Confirm->postProcess()
#21 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/StateMachine.php(164): CRM_Core_Form->mainProcess()
#22 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/QuickForm/Action/Next.php(61): CRM_Core_StateMachine->perform(Object(CRM_Contribute_Form_Contribution_Confirm), "next", "Next")
#23 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/HTML/QuickForm/Controller.php(203): CRM_Core_QuickForm_Action_Next->perform(Object(CRM_Contribute_Form_Contribution_Confirm), "next")
#24 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/packages/HTML/QuickForm/Page.php(103): HTML_QuickForm_Controller->handle(Object(CRM_Contribute_Form_Contribution_Confirm), "next")
#25 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Controller.php(353): HTML_QuickForm_Page->handle("next")
#26 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(312): CRM_Core_Controller->run((Array:3), NULL)
#27 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(86): CRM_Core_Invoke::runItem((Array:15))
#28 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm/CRM/Core/Invoke.php(54): CRM_Core_Invoke::_invoke((Array:3))
#29 /home/cac2member/public_html/wp-content/plugins/civicrm/civicrm.php(1133): CRM_Core_Invoke::invoke((Array:3))
#30 /home/cac2member/public_html/wp-content/plugins/civicrm/includes/civicrm.basepage.php(134): CiviCRM_For_WordPress->invoke()
#31 [internal function](): CiviCRM_For_WordPress_Basepage->basepage_handler(Object(WP))
#32 /home/cac2member/public_html/wp-includes/plugin.php(571): call_user_func_array((Array:2), (Array:1))
#33 /home/cac2member/public_html/wp-includes/class-wp.php(622): do_action_ref_array("wp", (Array:1))
#34 /home/cac2member/public_html/wp-includes/functions.php(877): WP->main("")
#35 /home/cac2member/public_html/wp-blog-header.php(14): wp()
#36 /home/cac2member/public_html/index.php(17): require("/home/cac2member/public_html/wp-blog-header.php")
#37 {main}