A fleet of new trains for services running to Ware could be delayed for up to a year.
Greater Anglia were due to start introducing the 111 new trains earlier this year, replacing their entire fleet of aging commuter rolling stock.
The class 720 Aventra trains are being built by Bombardier in Derby.
Similar class 710 Aventra trains used by London Overground were introduced in May 2019 - a year later than originally planned.
Managing Director of Great Anglia, Jamie Burles, told RAIL Mazazine that the problem relates to the Train Control Management System (TCMS), which is similar to the 710s used by London Overground.
The fleet replacement was part of parent company Abellio's bid for the East Anglia rail franchise, which runs from 2016-2025.