It seems that original avisnet.dll damaged (and shouldnt be renamed). When I tried to build C# and Basic Samples they couldnt read avisnet.dll file it didnt look like .Net or COM component. I simply deleted avisnet Reference and added Reference to AVLib.dll. File Interop.AVLib.dll was created in internal folders. Now all work. As I see avisnet.dll is the same as Interop.AVLib. Here what I tried: I renamed internal file Interop.AVLib.dll to avisnet.dll, deleted Reference to AVLib, added Reference to new avisnet.dll which I copied to AVBin. You couldnt believe, it doesnt work: file Interop.AVLib required but not found. Ha, rename avisnet.dll to Interop.AVLib.dll file and update Reference all work, of course.
So, I suggest dont use avisnet.dll at all. Just add Reference to native AVLib.dll. File Interop.AVLib will be created automatically. All will work. I think we shouldnt rename this file to avisnet.dll because program looks for exactly Interop.AVLib. And of course adding ActiveX files are also required as before.
If you want to have file avisnet.dll in AVin folder (for example, to show that .Net is supported :)) it must be named Interop.AVLib.dll but file will be unnecessary actually. You can research it.
A little bug in .Net samples