When you open a page and you see this error:
This error means that the Cross List web part was added to the page, but has not been configured to work with any lists in your site. Make a note of the page you are on (its address/URL) and contact your site admin to let him/her know that the web part needs to be configured by someone with the permission level of at least Designer in your site. You can also point out that instructions for configuring can be found here.