How to recreate busytime.nsf:
Busytime.nsf is the free time database on a non-clustered server. To rename the busytime.nsf file, do the following:

1. If possible, map a drive or FTP to the Domino server’s Data directory.
2. In Domino Administrator, open the live console and issue the following commands:

tell sched q
tell calconn q
tell RnRMgr q (Domino 7 and later)
dbcache flush

NOTE: Several “dbcache flush” commands may be required depending on the operating system and server load.

3. In the Domino server’s Data directory, locate busytime.nsf and delete it. Busytime.nsf contains no historical data so there is no reason to keep it when rebuilding.

4. Issue the following commands (not case sensitive):

load sched
load calconn
load RnRMgr (Domino 7 and later) 

How to recreate clubusy.nsf:
Clubusy.nsf is the free time database on a clustered server. To recreate or restore it, do the following:

NOTE: This process must be done to all servers in the cluster to avoid replication. Please see the following link for instructions on sending a command to multiple servers at one time.
http://www-10.lotus.com/ldd/dominowiki.nsf/dx/Tip__Send_the_same_server_command_to_multiple_servers_at_once

1. If possible, map a drive or FTP to the Domino server’s Data directory.
2. In Domino Administrator, open the live console.
3. Shut down the Sched and Calconn tasks on all clusters and flush the database cache with the following commands:

tell sched q
tell calconn q
tell RnRMgr q (Domino 7 and later)
dbcache flushNOTE: Several “dbcache flush” commands may be required depending on the operating system and server load.
4. On the Domino server’s Data directory, find clubusy.nsf and delete it. Clubusy.nsf contains no historical data so there is no reason to keep it when rebuilding.

NOTES:

• • Steps 3 and 4 must be done on ALL clustermates before Step 5 is performed on any server. Otherwise, old data may be added back into the clubusy database and invalidate what you are trying to do. If you do not do this correctly, you must restart the process for clubusy.nsf over again.

5. Issue the following commands on all clustermates (not case sensitive):

load sched
load CalConn
load RnRMgr (Domino 7 and later)