When the system fails to locate an assembly, it generates a log file. The Assembly Binding Log Viewer (Fuslogvw.exe) is a viewer program you can run from the command line that gives you access to this log. This log information helps you diagnose why the .NET Framework cannot locate an assembly at run time. Here's a tutorial on Fuslogvw.exe from the .NET Framework Tutorials.

George Shepherd, Syncfusion, and Stuart Celarier, Fern Creek