Comment 3 for bug 576941

I've got the same trouble on Windows7. The trouble as gone away doing this :

    Load up task manager (right click taskbar and select Task Manager)
    Go to the Processes Tab
    Select rdpclip.exe
    Click End Process
    Go to the Application Tab
    Click New Process
    Type rdpclip
    Click Ok

Source : http://www.gfi.com/blog/copy-paste-working-remote-desktop-connection-whats-wrong/