AE does not start after failover.

Document ID : KB000115887
Last Modified Date : 05/10/2018
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Issue:
After a failover of MSSQL Server cluster to second node, the Automation Engine will not come online. 

Error messages received in the WP logs upon startup attempt:

U00003591 UCUDB - DB error info: OPC: 'SQLExecDirect' Return code: 'ERROR' 
U00003592 UCUDB - Status: '42S02' Native error: '208' Msg: 'Invalid object name 'UC_VERSI'.' 
U00003592 UCUDB - Status: '42000' Native error: '16945' Msg: 'The cursor was not declared.' 
U00029108 UCUDB: SQL_ERROR Database handles DB-HENV: 1286f90 DB-HDBC: 1287070 
U00003591 UCUDB - DB error info: OPC: 'SQLExecDirect' Return code: 'ERROR' 
U00003592 UCUDB - Status: '42S02' Native error: '208' Msg: 'Invalid object name 'ovw'.' 
U00003592 UCUDB - Status: '42000' Native error: '16945' Msg: 'The cursor was not declared.' 
U00003526 UCUDB: Database version ('0.0.0') does not match your program version ('12.2.0'). 
00003591 UCUDB - DB error info: OPC: 'SQLNumResultCols' Return code: 'ERROR' 
U00003592 UCUDB - Status: '42S02' Native error: '208' Msg: 'Invalid object name 'ABLOB'.' 
U00003592 UCUDB - Status: '42000' Native error: '8180' Msg: 'Statement(s) could not be prepared.' 
U00003620 Routine 'UCMAIN_R' forces trace because of error. 
U00003590 UCUDB - DB error: 'SQLNumResultCols', 'ERROR ', '42000', 'Statement(s) could not be prepared.' 
U00003590 UCUDB - DB error: 'SQLNumResultCols', 'ERROR ', '42000', 'Statement(s) could not be prepared.' 
Environment:
UCUDB: Database version ('0.0.0') does not match your program version ('12.2.0'). 

Via SQL Server Management Studio, attempting to access the correct database with the user defined in the sqldriverconnect string: 

The database DatabaseName is not accessible. (ObjectExplorer) 
Cause:
The issue, in the originating case, was a problem with the MS SQL cluster node fail-over. The Automation Engine failed to start because of access issues when the cluster failed over. 
Resolution:
Switch back to the first, working node and start the Automation Engine.