Anyone who has developed a package for Visual Studio has run into the dreaded package load failure. Even after you ship you can have customers that run into this issue because the customer may be experimenting with beta releases of products that my break your package. This issue has risen enough for us internally that I'm blogging three things you can do to look for clues on what went wrong.
1. Turn on Visual Studio Logging
2. Turn on Fusion Logging
5. Restart Visual Studio and repeat actions that caused the package load failure
6. Look in directory c:\fusion-log or whatever custom log path you chose for clues
3. Run Depends on the assembly
Dr. Ex has blogged on the same topic with some additional things to try.