Restart the computer, close any running programs, and then try installing again. Some antivirus software might interfere ...

Restart the computer, close any running programs, and then try installing again.
Some antivirus software might interfere with the service pack installation. Try temporarily disabling your antivirus software. You can usually do this by right-clicking your antivirus icon (which typically appears in the bottom right-hand corner of the computer screen) and clicking Disable. If you disable your antivirus software before you install the service pack, be sure that you are aware of the risks involved, and be sure to enable it after the service pack is installed.

If closing any running programs doesn't fix the problem, visit the Microsoft website for more information.