The message Resetting standby activation ID 0 (0x0)" is a normal message after switchover. It hard to think about a problem with so little details. Check this metalink note, this might help. There was also a similar kind of bug but in 10.2.0.4
11.2 Data Guard Physical Standby Switchover Best Practices using SQL*Plus (Doc ID 1304939.1)
There was also a similar kind of bug but in 10.2.0.4. Workaround is to reboot the database. You can try rebooting the database. It might fix the issue.
This should be confirming the End-of-Redo on the standby. The 0 is in all of mine regardless of age of system ( changed MS )
Was able to find the exact same message on my test standby
Resetting standby activation ID 0 (0x0)
Media Recovery End-Of-Redo indicator encountered
Media Recovery Continuing
All my Standby's have it
Does not appear to be an issue.
Some more details here:
Message was edited by: mseberg