[Chimera-users] Adding Missing residues

Dear Chimera Users, I am trying to add missing residues to the protein with the ID: 1u54 But unfortunately for chain A, I cannot do the adding. I go to "Tools > Structure Editing > Model/Refine Loops". Then I choose "chain A" and I select "all missing structure" and then "apply". But I got an error. Is there any other way for it? for "chain B" it works. Best Wishes, Armin -- Armin Hodaei Department of Physics, Faculty of Arts and Sciences Koc University, Istanbul