You should see a first chance exception under the debugger. The failure happens when OLE tries to make a copy of the data because of the default is copy = true on SetData. If it is set to false it will just work in process as we don't actually have to serialize the type.

@JeremyKuhne If what is set to false?

copy when you manually put data into a DataObject first. https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.clipboard.setdataobject?view=windowsdesktop-9.0#system-windows-forms-clipboard-setdataobject(system-object-system-boolean)

We probably should have created an overload so you didn't have to manual steps. Here is what SetData does:

https://github.com/dotnet/winforms/blob/e36dddda003a9efb1e209c1a1ebc848f080b5d55/src/System.Windows.Forms/System/Windows/Forms/OLE/Clipboard.cs#L433-L440

So, to avoid the copy you have to turn SetData(format, data) into SetDataObject(new DataObject(format, data), copy: false). Then if things aren't consumed external to the process it won't need to serialize. If copy is true, the serialization is preemptive to allow the data to persist if you close the application.

No longer works "by default".

To see the failure, you have to catch first chance exceptions under the debugger to see it fail on OLE trying to retrieve a copy of the data (which happens when you set if copy == true, the default, otherwise on get).

The same procedures and switch are used for WPF. If you happen to have both WPF and WinForms in the same project, both Clipboard classes will be enabled.