This warning is generated by Riviera-PRO when some of the signals cannot be displayed in the waveform.
To get internal signal visibility, you have to set the read access to internal signals.
Go to Tools | Preferences | Simulation | Access
NOTE: For more information on the Access category, see the Riviera-PRO User Guide | GUI Reference | Dialog Box Reference | Preferences Dialog Box | Simulation Category | Access Category
Click on the icon to specify the access with the drop-down menus
Click Apply and then OK
Use the +access +r switch for the asim command. For example:
asim +access +r ...