Office error `Office Software Protection Platform`?

I'm having this errors when trying to install office.

How can I fix this?

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Error 1923 can be a bit vague but was intended to mean that a previous version of office was found on the system and is creating a conflict. Here's the official MS solution:

To work around this issue, restart the computer after you remove the prerelease version of the 2007 Office programs.

However you may not actually have a previous version as there are a few of other things that can cause this, such as aggressive anti-virus or, as Matt pointed out, insufficient privileges.