If you are entering commands in a command prompt that requires administrator privileges, you need to start an administrator session.
Go to Start / All Programs / Accessories. Right click the Command Prompt and select the 'Run As Administrator' option. Click Continue on the UAC prompt.
When you are installing an application, you may need to do the same thing for some installation programs. Right click the applications installation file and select the 'Run As Administrator' option.
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Ronnie Vernon
Microsoft MVP
Windows Desktop Experience