That error seems to indicate "something" is blocking access to GSX *own* installation folder, which of course is not normal, since the installer has created the folder itself. The only thing that can possibly do that is the antivirus so, just do as follows:
- Configure the antivirus and add the whole Addon Manager folder to the Antivirus Exclusions.
15GB on the Windows temporary folder is not much ( you are at risk of crashes with so little space left, it's enough the Swap file would grow a bit larger than your RAM, and it will surely crash Windows if it happens ) so, the first thing to do, is using the Windows free space Wizard to see if it can help you free some extra space, perhaps removing unused temporary files.
So I just selected the FSDT folder in Explorer and hit delete and it went through the whole bar progression process of deleting items, finished normally, but the FSDT and all of its contents were still there! I can cut and paste out and it seems delete individual folder/files within the Addon Manager folder, but not the Addon folder itself. I am reluctant now to go through deleting every single item by hand.
This report indicates the antivirus that has blocked the GSX installer access to its own folder, has blocked access to YOU as well, so it won't let you remove the whole FSDT folder.
To uninstall everything and try again after you fix your pesky intrusive antivirus, you should do as follows:
- Uninstall the FSDT Installer from the Windows Control Panel. Yes, it's there, it's called "Fsdreamteam Universal Installer". Doing this from the Control Panel, will allow you to select a
different folder for the next reinstallation so, if you have another drive with lots of space available, you can use that instead, so you might be able to complete the installation even with only 15GBs left on C:, which in that case will only be used to uncompress temporary files, and the space will be reclaimed at the end.
- If you still have the Addon Manager folder, try to remove it manually and, if you still can't, REBOOT Windows and try again.
- Now you can reinstall the FSDT Universal Installer and, this time, if you have another drive with more space, select THAT as a destination instead of c: As an example, if you have a drive named D:\, just select D:\ and this will result in all FSDT products ending in D:\Addon Manager, and this is perfectly fine, since we only use Symbolic links to the Community folders, and only for folders that needs that, so the location of the Addon Manager itself, is completely irrelevant to where you installed MSFS.
- Be sure you add this new folder ( assuming you installed in a new folder this time ) to the Antivirus EXCLUSIONS.
- After the FSDT Universal Installer, you can now installing GSX Pro again.