You have downloaded latest iTunes, but when you try to install it, you get an error message: “The Windows Installer Service cannot be accessed. This can occur if you are running Windows in safe mode, or if the Windows Installer is not correctly installed. Contact your support personnel for assistance.” You are not running Windows in safe mode.
Log on to your computer as an administrator. Click your “Start” button, and then click “Run”. In an “Open” box, type CMD, and then click OK.
At a command prompt, type “msiexec.exe /unregister” without quotes, and then press ENTER. Type “msiexec /regserver” without quotes, and then press ENTER. Verify that a SYSTEM account has full control access permissions to a HKEY_CLASSES_ROOT hive in a Windows registry.
In some cases, you may also have to add Administrator accounts. Click your “Start” button, then click “Run”, type regedit in an “Open” box, and then click OK. Click a following registry hive: HKEY_CLASSES_ROOT
On an “Edit” menu, click “Permissions”. If SYSTEM is not listed in a Group or user names list, click “Add”. Make sure that your local computer name appears in a “From this location” box.
Type “system” in an “Enter the object names to select” box, click “Check Names”, and then click OK. Click SYSTEM in a Group or user names list, and then select a “Full Control” check box under “Allow” in a Permissions for SYSTEM box. Click Apply, click OK, and then quit Registry Editor.
Make sure that a SYSTEM account has full control access permissions to a HKEY_CLASSES_ROOT hive in a Windows registry. I have included a sample image of what security permissions for a HKEY_CLASSES_ROOT hive should look like. Click on “SYSTEM” under “Group or user names”: when editing that hive in Windows registry.
“Permissions for SYSTEM” should have check marks under “Allow” for “Full Control” and “Read”. If a “SYSTEM” entry does not exist under “Group or user names:” then please follow instructions below to add it. On an “Edit” menu, click “Permissions”.
If SYSTEM is NOT listed in a “Group or user names list”, click “Add”. Make sure that your local computer name appears in a “From this location” box. Type “system” in an “Enter the object names to select” box, click “Check Names”, and then click OK.
Click SYSTEM in a Group or user names list, and then select a “Full Control” check box under “Allow” in a Permissions for SYSTEM box. Click Apply, click OK, and then quit Registry Editor.