Here's an example of how a tiny bit of digging saved me hours of confusion recently when I hit an unusual edge case. I was doing a build of sample that was showing C# interop-ing with IronPython, but I was using a daily build of .NET 4 and a random build of IronPython.IronPython in Action which is nice.
I made a mistake and had some really old DLLs floating around that I shouldn't have had. My symptom was a FileNotFoundException for the file "System.Dynamic.dll." I KNEW it was in the GAC (Global Assembly Cache) and I could SEE it as a reference DLL in my directory. Can't find the file? Dude, it's right there!
ZedGraph charting library examples from C# to IronPython.