Transient choking occured at Junction X. The set point could not be met.

Full Message text is:

Transient choking exists at junction X. The specified flow or pressure could not be met.

This warning tells the user that choked conditions exist at a junction with a specified pressure or flow rate, specifically that those choked conditions existed during the transient simulation. In this situation, xStream will limit the flow at the pipe to the choked flow rate regardless of the user-defined conditions.