Solutions/Cannot add members to ring group after upgrade
From FusionPBX
Short Answer
You did not run 'App Defaults' when you upgraded see Upgrade FusionPBX/4.x for correct upgrade instructions.
Why
The number of new boxes to display were moved to a default setting to allow customization. If you upgraded the source without running 'App Defaults' those settings are effectively 0 causing them not to display.