# Error: Session selection is required for one of the selected units

This error message will occur upon enrolling on the sessions' class and group specified in a Scheduled Unit. Check the **Session Group** and **Session Class** logic of the Scheduled Unit. If you are using Rapla, refer to the [Rapla Knowledge Base](https://docs.silverband.com.au/home/v/rapla/example-events/session-group-and-class). If the issue is just on one Scheduled Unit, you can directly check and edit the necessary error with your Group and Class value coding within Paradigm, *see* [**Edit Sessions**](https://docs.silverband.com.au/home/paradigm-knowledge-base/academic-scheduling/workflows/manage-sessions/edit-sessions).