This message simply means that write operations to the directory have been paused temporarily. This occurs when the MCS or BARS backup utility or any other type of backup, does its backup of DCD. A few minutes later you should see an event where the directory becomes unquiesced.
Sometimes you will see those messages during, or right after the backup application has completed. The 'Quiesced' is telling us that DC Directory cannot get the resources from the server because some other process is hogging the resources. Basically, this is CallManager 'pausing' the DC Directory service until it completes what it is doing.