Cannot install Thunderbird, get message "you may not have the necessary permissions to use all the features of the program you are about to run. You may run this program as a different user or continue to run the program as the current user". I am the ONLY user of this computer with administrator privileges. All other programs install without problem. I have disabled my anti-virus and firewall, and deleted previous Thunderbird installation and deleted folder in program files (x86). WTF???