This can happen if the Mail app was moved from Applications to another location, such as the desktop, before installing the Security Update.
- 

- Hold down the Option (⌥) key and choose Apple () menu > System Profiler… to open System Profiler. 

- Click "Applications" in the "Software" section. Note: The spinning gear in the top middle indicates a search in progress. Once completed, sort by application name and look for "Mail" to see all copies. 

- Make sure Mail is located in the Applications folder. If it is not, drag it back there and enter an administrator name and password if prompted. Tip: Choose Go > Applications in the Finder to easily open the Applications folder. 

- After moving Mail back to Applications, follow these steps

- 

- Download Safari 5.1.7 for Snow Leopard 

- Reinstall the Mac OS X Update v10.6.8 Combo v1.1 

- Reinstall Safari 5.1.7 for Snow Leopard 

- Reinstall Security Update 2012-004