Re-order (fast busy) tone: The most common reason for receiving re-order (fast busy) is that the calling party does not have the rights to call the called party.
A re-order tone can be caused by these various Calling Search Space (CSS) and partition configuration issues:
The calling phone does not contain any CSS, but the called phone is in a partition or the calling phone has CSS configured, but the called phone is in a different partition other than the configured CSS.
To resolve this issue, ensure that the calling party's phone contains a CSS that includes the called party's partition.
The calling phone has CSS configured, but the called phone is not in any partition or the calling phone does not contain any CSS nor does the called phone's directory number belong to any partition.
The configuration appears acceptable (the calling phone's CSS includes the called phone's directory number partition).
To resolve this issue, try resetting the CSS, partition and both phones involved. If the failure still occurs, perform the steps in the Set Up Cisco CallManager Traces for Cisco Technical Support document.
For more information on CSS and partitions, refer to these documents: