I am experiencing this same problem. Sorting by user-meta works on a standalone WP installation but returns no results in a multi-site installation.
Thank you for any assistance you can provide.
While my previous post did solve the “Invalid type specified” problem while linking to uploaded files, it had the effect of creating a similar problem while browsing the server for uploaded images.
I now believe the actual problem is in this file: ckeditor-for-wordpress/filemanager/browser/default/frmresourcetype.html
Beinning at line 37:
var aTypes = [
['File','File'],
['Image','Image'],
['Flash','Flash'],
['Media','Media']
] ;
Should be:
var aTypes = [
['Files','File'],
['Images','Image'],
['Flash','Flash'],
['Media','Media']
] ;
