codeigniter 3 file upload not working on iis

It's usually a file directory security problem, as the IIS user don't have write access to your upload folder.
You can fix it like this:
Right click on upload folder
Properties
Security
Edit
Select "Users (COMPUTER\Users)"
Check "Modify" and "Write"
Ok
Ok

If you don't want all users to have write access, you will need to find what user account IIS runs under (I got no idea).

It worked thank you so much.