This problem generally occurs when a process locks clipboard for reading and writting and didn’t release it properly. Clipboard will function normally after killing that process. The tool (GetOpenClipboardWindow) will help you to identify the culprit process. Download this tool now and share it with users.
From my experience, I can say that mostly mstsc.exe is the process which blocks the clipboard. The reason I assume here is simple because it dealts with clipboard of connected computer and your computer.
Happy Learning..,
Sitaram Pamarthi