Unable to Activate Exchange 2010 Mailbox Database "Error: content index catalog files in the following state: 'Failed'.

Issue:
you attempt to move the active copy from a mailbox DAG Member server to another server you get error:

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Microsoft Exchange Error
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Cannot activate database copy 'Activate Database Copy...'.

Activate Database Copy...
Failed
Error:
An Active Manager operation failed. Error: The database action failed. Error: An error occurred while trying to validate the specified database copy for possible activation. Error: Database copy 'DB1' on server 'dag01' has content index catalog files in the following state: 'Failed'.

To Resolve this issue re-seed the Content Index:
1. Restart the MSExchange Search service on the node which has the active database.
2. Run update-mailboxdatabasecopy -catalogonly on each passive DAG Member
3. Activate Required Database

e.g. Command
update-MailboxDatabaseCopy -Identity "DAG01-DB10\DAGMB02" -CatalogOnly

This will seed from Datatabase DAG-01\DB10 to Passive Server DAGMB02