People with missing parts problems, this may be the solution to your problem. I would like to add a little to semanticman's revised definition of the installation instructions that ended up resolving the infamous "missing parts" error for me. I had struggled with this for a few days before I got it right (even went through each .cfg file for each part to redefine the model mesh and texture in the asset parameters in order to get it to work, which it did but was a laborious process). The thing I would like to add/point out in the following instructions is the word CONTENTS. Most of the people and myself having troubles installing the mod probably made the mistake of copying/extracting the 'gamedata' folder from the B9 Aerospace .zip in the 'gamedata' folder in the KSP directory. You want to copy/extract the CONTENTS of the B9 'gamedata' folder, not the folder itself. The missing parts won't appear if their parent 'gamedata' folder is in another 'gamedata' folder. My guess as to why this is is due to the way the model files are linked to their corresponding part in the .cfg file's asset parameters of the parts folders where there are multiple .cfg files such as 'Aero_HL_Body' where there are 10. I imagine it was set up this way to cut down on size eliminating the need for duplicate files. This is what your ksp 'gamedata' folder should look like with B9 installed correctly. Hope this helps