VC6.5: DB lock has been detected on the database by the user associated with the provided DSN.

This is caused by either the vCenter schema is not completely created or the schema session is locked by something else. If you know that the possible locked session is all you need to get rid of then do the following query.
Or
Bouncing the database instance took care of it.

SYS> select 'alter system kill session ''' || sid || ',' || serial# || ''';' from gv$session where username ='VPX';

'ALTERSYSTEMKILLSESSION'''||SID||','||SERIAL#||''';'

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alter system kill session '240,4292';

SYS> alter system kill session '240,4292';

System altered.