ATI 2009: "Silent mode" doesn't work properly

I use ATI 2009 with WinXP SP3, fully updated. I do an incremental backup of a directory on a network drive every 2 hours to my PC's HDD. Sometimes I'm using a file in that network directory. I want ATI to ignore this, and I've specified "silent mode", but I still get an error message that the file is in use, and I must click "Ignore". Unattended backups don't complete properly.

The first time this happened during a back, ATI paused and put up an error message, and I clicked "Ignore", and ATI resumed. I then edited the backup job, under "Backup Options"-"Error Handling", where I selected "Do not show messages and dialogs while processing (silent mode").

I stopped the current backup, exited Acronis, then restarted Acronis and confirmed that my selection was still there. Then I started the backup again.

HOWEVER, the error dialog still comes up and the backup is paused!

It seems that this "silent mode" isn't working correctly.
Can anyone help? I would very much appreciate it.

Many thanks!