When items get put into the 'Failed to Store' folder it's because there was problem with the Storage Service. My guess is that purging the Storage Archive queue is what caused these messages to be sent to the 'Failed to Store' folder. Nothing to wor...
Having so many items in the Storage Archive queue stands out as a problem to me. In my experience you rarely, if ever, have items there. I wouldn't reccomend purging the Storage Archive queue.
What type of storage is the Vault Store Partition? If it...
A Global Catalog Server can be specified in the Vault Admin Console under Targets>Exchange on the Properties of the domain target.
You could also try logging on to the EV server with the Vault Service Account credentials and checking the "DS Serve...
You say that replication is in place, but I'd start by checking that Centera replication is working. I think the only time I've seen this is when there is an issue on the Centera side.
Vault Cache uses Migrator Server. You could try restarting all the EV services and turning on dtrace for the processes you see referenced in the Event log in the Category field.