A skeleton is a structure used in assemblies to control the parametrics and dependencies inside Pro/E. Think of the skeleton as a Christmas tree and the models as the ornaments. If you stack ornaments on a table, one on top of the other, then remove the bottom one the whole assembly falls apart. On the other hand if you assemble the oraments to the tree (or skeleton) and remove one of the base models the others will still remain on the tree. You could also wiggle the branches of the tree to provide movement in the assembly. Seletons are a must for good assembly management! However, with that said, the skel extension on these files is not picked up by some builds of intralink and is also build sensative between releases. For this reason we make our skeletons in standard part file format and assemble them in as the first model. Since you recieved this model from someone else chances are you have a build conflict, try opening without using Intralink and switch to the build of the provider. I hope this helps. If not repost and I'll try to help.
