I purchased this game from GOG, downloading is no problem. When it comes to installing I get this message "Unable to execute file in temporary directory. Setup aborted. Error 5: Access is denied. I'm administrator of the user account on this pc.. I'm the only account. My OS is Window 7 64-bit. I'm at a lost as to why this is happening.
Any help will be appreciated.

Try suggestions posted or [url=https://answers.microsoft.com/en-us/windows/forum/windows_7-performance/unable-to-execute-files-in-the-temporary-directory/0d441663-6167-420d-b936-53f9c3d17898]here

Try right-clicking the installer and select "Run as administrator".

If prompted by User Account Control (UAC), then click on Yes to apply permission to allow the program to run with full permission as an administrator.

I have done that. Another strange thing is that I downloaded Dungeon Keeper and Dungeon Keeper 2 and they installed with no error message. I never have been prompted by User Account Control.

Thank you for your reply.

Hmm, so DK and DK2 installed properly but M&M8 didn't. Try copying the installer to another location and run it from there, also with admin rights (right-click => Run as..). Disable anti-virus software and don't install the game into the Program Files folder but into a custom one on C: (e.g. C:\GOG.com\).

Turning off anti-virus software WORKED!!!! Thank you very much.