Sophos Anti-Virus for Mac OS X: 'Scan this Mac' item fails to scan

Issue
The 'Scan This Mac' item in the shield menu either does nothing or produces an AppleScript prompt 'Where is Sophos Anti-Virus'.

This issue is seen following a clean install or upgrade to Sophos Anti-Virus for Mac OS X, version 7.0.5, when a different user logs on via fast user switching, and the Sophos Anti-Virus GUI has not yet been launched by this user.

Sophos product and version
Sophos Anti-Virus for Mac OS X, version 7.0.5

Operating system
Mac OS X versions 10.4 and 10.5

What to do

The following workaround will fix this issue:

• Launch the Sophos Anti-Virus GUI and select 'Scan This Mac' from the menu bar item.