This is just because of old version of symantec residing on your computer. Even when while unstalling it will give the same error. Follow below steps :

1. In Add or Remove Programs select Symantec Antivirus, and then click Change.

2. Select Remove.

Symantec will be uninstalled. :)

3. Delete all symantec related folders from Program Files, Common Files and Documents And Settings.

4. Try the installation again.

5. It will work. Atleast it worked for me.