Popup stating:
"The selected item could not be restored. Enterprise Vault is not available. Try again later."
Client Log Trace:
~CItemMarker::MarkRestoreMe: 0x8004060C
The hex code 0x8004060C is a MAPI error which translates to MAPI_E_STORE-FULL. This means that the mailbox has reached it's quota limit therefore the item cannot be restored.
Increase the quota storage limit in Exchange or delete some messages to free up space on the mailbox.