A player cannot be in two periods at the same time.
If attempting to PIP athletes into a period, whilst already PIP'd into another, the below 'already exists in concurrent period' error message will occur.
This error message will show the concurrent period in which the athletes are already 'PIP'd into. To resolve this, either remove the athletes from the current period or edit the new period's start and end time to not overlap with the current period in which the players are in.
If you cannot find this period within the current Activity, an athlete might also be 'PIP'd' into a period from another Activity that happens at the same time.
If this is the case, open the simultaneous activity and remove the player from the periods causing issues. Once the athlete is removed, please reprocess this activity before returning to the alternate activity.
Please see this guide for more information on Periods: How to Create, Edit and Delete Periods
If you are unable to locate the period that is causing issues, the activity may have been deleted. If this is the case you can use Activity Admin to restore the activity. You can then remove athletes from the period.