This morning I ran into a ASP.NET bug in Visual Studio. Dragging a custom server control on an aspx file was not possible since I had ‘an invalid FORMATETC structure’ (what the …. is that?!). The message box alerting me something is really really wrong is this one:
Trying to solve the bug, I found the following attribute to be the problem: [ToolboxItem(true)]. Just delete the attribute, rebuild the application and the problem/bug disappears!
Good luck! Happy coding!