Installation file missing error

If you try to install SQL Server Express you may receive the following error message:
Installation file missing: WindowsInstaller-KB893803-v2-x86.exe SQL Server Express installation failed.

You may also have issues with installation of any other applications, because of installation file missing error.

This problem is related to MSI Installer not working properly.

To solve this please do the following:

1. Log on to your computer as an administrator.
2. Click Start, and then click Run.
3. In the Open box, type cmd, and then click OK.
4. At the command prompt, type msiexec.exe /unregister, and then press ENTER.
5. Type msiexec /regserver, and then press ENTER.
6. Verify that the SYSTEM account has full control access permissions to the HKEY_CLASSES_ROOT hive in the Windows registry. In some cases, you may also have to add Administrator accounts.