From vSphere 5.1 Release notes
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Insufficient privileges error occurs when you use manually created DB2 database users
When you install vCenter Single Sign On and the installer requests Single Sign On database information for existing databases, you can select the Use manually created DB users check box. If you are using a DB2 database and have manually created users with the rsaIMSLiteDB2SetupUsers.sql script, you might receive an error that the database users do not have sufficient privileges.Workaround: The rsaIMSLiteDB2SetupUsers.sql script, which is located in the <installation directory>\Single Sign On\DBScripts\SSOServer\schema\db2 directory, does not include two of the required privileges. If you use the script to manually create users, edit the script to include the following privileges:
GRANT DBADM ON DATABASE TO USER RSA_DBA;
GRANT CREATETAB ON DATABASE TO USER RSA_USER;
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More info here