Written
When developing forms with file uploads you will sometimes get error messages referring to JFolder or JFile. These are usually because the permissions are not correctly set on the upload folder.
The folder should probably have a chmod setting of 755 or possibly 777 (check with your web hosts documentation).
If the permissions don't resolve the problem please check to see if FTP is enabled in your site Global Configuration. If it is, then disable it temporarily and re-test.
Joomla! will try to use FTP if it is enabled, but the FTP user on the server may well have different permissions from the Joomla! user (these are server users not to be confused with registered site users).