When you run the 'Protect computers wizard' in the Console, a list of computers onto which you can install is created. This list comprises those computers that can have a scheduled task assigned to them by the Microsoft Task Scheduler. Computers that cannot be protected automatically include those running Windows 95/98, Mac OS X and Linux. Example:
Computers that cannot be assigned a task by the Microsoft scheduler can have the installation performed manually. You can then manage them using the Console.
The Windows components may have been disabled as part of a system security policy. Check before changing your network setup.
What To Do
To manually install software see:
If the computer is running a modern Windows operating system (i.e., Windows 2000/XP/2003/Vista/7/2008/2008 R2/8) follow the step on the Sophos endpoint deployment guide to ensure your network settings have been correctly configured.