Error message

[chancer]

chmod changes what the user, the group, and the rest of the world can do. chown lets you make sure you have the correct user and group in the first place.

The php error message you are getting is a typical ownership challenge. It's saying to me that somehow you have uploaded files into that directory owned by the wrong user or by the wrong group or possibly both. The web user needs to be in there for a php script to work properly. For instance, if you've gone in there as admin or root and uploaded files, ownership on any *nix system will default to admin or root. But the Apache web server is not configured to serve files owned by admin or root.

I'm not sure if you can do this via ftp, you may need shell access to the server, but I'd try it in ftp first anyway. Just check that the file throwing up the faults is owned by the same user and group as files and scripts that are working.

By the way, this is also a typical sysadmin mistake. If you've had assistance from your web host, they may have changed something and forgotten to re-set ownership.