Error message – The file wp-config.php already exists.

After copying/migrating site from a sub folder – domain.com/blog to the root – domain.com, I get the message –

The file wp-config.php already exists. If you need to reset any of the configuration items in this file, please delete it first

The wp config file is already there because its migrated etc.

If I view the site in a browser with all cache cleared, site loads fine but not on browser which already visited the site.

Could be a potential issue of people have visited the site in the past and something is cached. Its happened 2-3 other times – may just be a coincidance and nothing specifically to do with All in One??