Why can't I single-step Clipboard-code within the VS.NET debugger ?

Answer 1

I've never looked into this, but it's easy enough to guess:

1. The clipboard is a shared resource
2. Only one app (per desktop) can "own" the clipboard at any given point in time
3. Your app owns it (after calling OpenClipboard())
4. VS wants it (probably because, among other things, it's an editor)
5. While your app is stopped at a breakpoint, no amount of waiting will ever find the clipboard not owned by your app.
6. Hilarity ensues!

Answer 2

Don't waste time suspecting it's a .NET thing. At times, the relation between Visual Studio.NET and the .NET runtime is like ActiveX and ActiveDirectory - it tells you which marketeer was involved, Visual Studio.NET in fact has a number of debuggers. Native, script, or managed - only the latter is really .NET-related. You will be using the Native debugger.

If you want to investigate, I suggest hooking OpenClipboard using Microsoft Detours, then running your app in the debugger. You'd be able to see who is competing for the clipboard.