Description
You may this error when compiling a design in the Quartus® II software or running the MegaWizard™ Plug-In Manager while using VNC. The message indicates that the session manager for VNC was trying to save the state of the Quartus® II software in the event that the user logs out while the Quartus II software is still running. This behavior is not supported by the Quartus II software, and the error message can safely be ignored.
Resolution
You can disable the message from appearing by running the command
unset SESSION_MANAGER
Note that this command will completely disable the session manager from running.