You are unable to open the Top Down Planning out of the box portlet, receiving an "Error 501 - Not Implemented. The server does not support the requested feature. Contact your system administrator."
Release : 16.0.2
Go to Administration > Studio > Content Add-Ins > System: PPM content > Items.
Find and select "Top Down Planning by Investment" (projmgr.topDownPlanning) and click on Install. You will get an "Alert:This action will overwrite (undo) any customizations you have made to these items. The content items below will be installed. If the selected items have dependencies, some items may be added to the installation list. Do you want to continue?".
Click "Yes" and the Portlet will be reinstalled to the current out of the box version.