I have installed ARTEEditor for Sharepoint (MOSS 2007). For the site collection administrator user there is no problem using ARTEEditor, everything works fine. If any other user (Wiki Member = Contribute or Wiki Admin = Full Access) tries to edit the wiki page, ARTEEditor opens a login window and keeps asking for user/password, eventually failing.
This error occurs when the ARTEeditor folder does not have the same permissions as the SharePoint Group your Site Collection Administrator is a member of. Navigate to the ARTEeditor folder within the Virtual Directory folder on your server that relates to your SharePoint application, right click to bring up the properties of the folder and make sure that the following groups are added under the security tab:
AUTHENTICATED USERS (of the server with only Read permission)
And any other members or groups that are specific to your SharePoint application.