Is this a central quarantine database that clients submit to? If so, are the clients then quarantining locally instead of on the central db? If so, they may not be able to connect to the central db due to some kind of network connectivity problem or blocked IP ports. Have you checked that the requisite ports are still open?
Have you checked the size limits in the quarantine db properties?
The few problems we've had with central quarantine have been a result of client settings, network connectivity issues, & one firewall issue. Good luck with your problem.