FS2004 Library Creator/mdl Tweaker error

Hi all,
can anyone assist with the following problem?
I have some gmax tree mdls that I want to remove shadows and unify normals.The gmax mdls load fine into library creator and run ok in FS. However if I run mdl tweaker on them and then try to create the bgl with library creator I get the following error:


I am sure it is something I am doing wrong but can't identify why it doesn't work.