When performing updates to the circulation module it is a good idea not to do any lending until the updates have been completed and checked.

The reasoning behind this is that before starting any update you MUST do a backup.  If there was a mistake made during the update and it is necessary to restore from the backup you only have the option of restoring catalogue data only, circulation data only or all data.

Senario -

1. The backup is done prior to any changes to Circulation information
2. Lending continues on the front circulation machine
3. A mistake is made whilst doing the updates
4. Circulation data is restored from the backup
5. ALL loans done after the original backup are LOST during the restore process

(More detail necessary)