Generally this error will only occur because a third party plugin has deleted the custom roles and capabilities that Connections installs and requires. Currently there are two know plugins that can cause this issue.
- s2Member
- Every time this plugin is updated, it will remove all custom roles and capabilities that are required by other plugins which includes Connections. More can be read about this in this FAQ.
- User Role Editor
- Clicking on the “Reset” button in this plugin will also remove remove all custom roles and capabilities that are required by other plugins which includes Connections.
This solution to fix this can be found in this FAQ.