O que eu encontrei:
This has to do with some application that's having a lock over the Windows Clipboard. David Candy's application should determine the Process that's causing the problem.
Download GetOpenClipboardWindow.zip from here: > http://windowsxp.mvps.org/temp/GetOpenClipboardWindow.zip
Unzip and run the tool. Post back what it reports. For best results, run this utility during the time you encounter the Copy<=>Paste problem.
Portanto, pode ser que algum programa esteja bloqueando sua área de transferência. Tente descobrir o que está causando o problema e informe-nos.