Access is denied / the file is in use by another process

What you see

• FiveM cannot write to its cache, update itself, or start
• A file operation fails part-way

What usually causes it

• A leftover FiveM/GTA process holding the file
• Antivirus or a backup tool holding the file open
• The folder is read-only, or owned by a different Windows account
• The game or FiveM is installed under a protected location such as Program Files with restrictive permissions

Worth checking first

• Check for leftover FiveM/GTA/Rockstar processes
• Check whether the folder is inside a synced or protected location
• Check Windows 'Controlled folder access' if it is switched on

Safe steps, one at a time

• Close leftover processes and try again (restarting the PC does this reliably)
• If Controlled folder access is on, add FiveM as an allowed app rather than turning the feature off
• Add the FiveM folder to antivirus exclusions — do not disable protection
• Only if the above fail, run FiveM once as administrator to test whether it is a permissions problem, then fix the folder permissions rather than continuing to run elevated

When to stop and ask staff

Never an AGN issue.