The installers will always run as Admin, regardless if you say it so or not so, that's not the issue.
This error can only be caused by one of these two reasons:
- You started the installer too quickly after closing a previous FSX session, without giving a chance for all the files and processes started by it to close down properly.
OR
- An external program, like an antivirus, is denying you access to the install folder. Many users are now aware they run multiple security-related software, so they must be all disabled and configured to exclude the sim folder from scanning.
First, try to reinstall after restarting Windows.
If that doesn't fix it, even if you are SURE the antivirus it's not running now and you are SURE FSX is not running, it might still have caused a mess in your file permissions, denying you from accessing a folder, while the antivirus was still active.
Yes, it seems strange, but I witnessed this first-hand on an user system during a remote assistance session. There are some free utilities you can try to unlock that folder:
http://www.iobit.com/en/iobit-unlocker.phphttp://www.freefileunlocker.com/And tell to the utility to unlock the FSX\fsdreamteam folder, then REMOVE IT manually, and then REINSTALL GSX.
