This happens if a program opens the clipboard, but never closes it. Until the clipboard is closed, no other application will be able to access the clipboard.
The Clipboard API and how applications use it is basically:
the clipboard can only be owned by a single application at a time. Typically, how a program pastes is to open the clipboard, retrieve the data, and insert it into the document. Then it closes the clipboard.
If a bug or other problem occurs that prevents an application from closing the clipboard for any reason- for example, maybe there is corrupted data and it throws an exception or an error occurs or some other logic error- it will keep the clipboard "owned" to itself, and any other application that tries to access it will not be given the clipboard handle.
To fix it, one "simply" needs to find out what application balls-up and close it. As part of the process termination, all open handles- which includes the clipboard handle it accidentally opened- are closed and destroyed.
On that note, I just slapped together a
small program that hopefully can be used if the clipboard has this issue to finger the culprit.
