I am glad to announce that Tina Yeh at MSI found the culprit. It seems that Modeller aligns all structures to the first one. In our case the first structure (which was not our primary template) had only 9 residues and, therefore, several of the other structures could not be superimposed on it. Making the primary template the first parameter of the "SET KNOWNS" command turned out to be the solution. Nothing else needed to be changed.
Thanks everybody for trying to help us out. It is much appreciated.
Cheers,
Pieter
Pieter Stouten || Computer Aided Drug Design Group || No good deed ever The DuPont Merck Pharmaceutical Company || goes unpunished P.O. Box 80500, Wilmington, DE 19880-0500 || Phone: +1 (302) 695 3515 || (Ferengi Rule Of Fax: +1 (302) 695 9090 || Acquisition #285) Internet: pieter.stouten@dupontmerck.com || Web: http://www.halcyon.com/stouten/ ||