I think this may be to do with permissions on the folder. Your permissions are not the same as php's permissions. The fix depends on what server you are using, but in a Linux server you can use a chmod command on the directory to change the permissions. You need write access for the Other group of permissions (the second-last bit). Use the command

chmod 766

to assign full access to the directory's owner, read/write access to the owner's group and read/write access to other users (which includes php/www).

I'm not sure about a windows server sorry, maybe someone else can help if you are using a windows server.