DLCworkshop02.esm can't be cleaned

[MrShadowBlood]

When I add apply filter for cleaning this pops up, A FILTER HAS BEEN APPLIED, THE TREEVIEW CONTENTS IS FOSSILIZED AND WILL NOT ADJUST STRUCTURE TO CHANGES, PLEASE REMOVE OR RE APPLY THE FILTER IF NECESSARY. I removed filter and appy it but it won't let me clean it. Any advice on how to fix this?