Source

Level

Description

The existing appointment with the subject <subject> in mailbox <mailbox name> was deleted. The start time, or both the duration and end time were missing.

Comments

 

We noticed this event after an employee ran the Symantec MS Blaster scan and removal tool on an Exchange server. Symantec would not confirm that they had any complaints about this behavior, but the scan and removal tool works just like their normal file level virus scanning tool.

As per Microsoft: "This behavior can occur if a file level virus scanner is scanning the installable file system (IFS) M drive of the Exchange 2000 computer, and may occur during a weekly or daily scan of the server. The virus scanner may be set to include all drives of the server. When the M drive is scanned, the items in the information store are treated as files. In this case, the virus scanner modifies a property or attribute of the calendar items, and as a result calendar items may be hidden. To resolve this behavior, stop any virus scanner from scanning the M drive. To recover lost calendar entries, either restore calendar items from a backup that was made before the calendar items were lost, or manually re-create the calendar items".