I've just installed Liferay Portal 6.1 RC1 using wizard.
Go to "Control Panel" -> "Server Administration"
Executing any of "Resources"-tab options ("Run the garbage collector to free up memory. ", "Clear content cached by this VM.", "Clear content cached across the cluster. " etc.) would cause a blank screen and "ERROR [PortletRequestProcessor:377] Forward does not exist" in server log.
A similarame problem occurs in "Users and Organizations" when deleting a user or an organization, but instead of blank screen the "Edit User/Organization" dialog is displayed.