This policy setting specifies whether to prevent the sharing of Clipboard contents (Clipboard redirection) between a remote computer and a client computer during a Remote Desktop Services session.You can use this setting to prevent users from redirecting Clipboard data to and from the remote computer and the local computer. By default Remote Desktop Services allows Clipboard redirection.If you enable this policy setting users cannot redirect Clipboard data.If you disable this policy setting Remote Desktop Services always allows Clipboard redirection.If you do not configure this policy setting Clipboard redirection is not specified at the Group Policy level.
Windows Components\Remote Desktop Services\Remote Desktop Session Host\Device and Resource Redirection
At least Windows Server 2003 operating systems or Windows XP Professional
HKLM\SOFTWARE\Policies\Microsoft\Windows NT\Terminal Services!fDisableClip