Cambridge-bound trains from an east Cambridgeshire village have been suspended because new rolling stock is too long for the platform.
Those wanting to travel west from Kennett near Newmarket will have to use a replacement bus service for the time being.
The reason is that new trains are not able to stop at some stations because their platforms are too short and they are only able to open some doors at present.
A new piece of software is due to be installed within a few weeks - but until then passengers heading east from Elmswell near Bury St Edmunds and west from Kennett are being taken by bus to the next station.
A Greater Anglia spokeswoman said: "We expect the software to be ready in the coming weeks.
"Given the many advantages of the new trains over our existing older trains, we considered it was best not to hold up the roll-out for one system and one supplier.
"We sincerely apologise to our customers for the inconvenience this temporary arrangement causes."
The new trains have more seats, plug and USB sockets, free fast wifi, air conditioning, better passenger information screens and improved accessibility features.
They are powered by diesel and electricity, and are much greener than the existing diesel trains, with lower emissions, and modern brakes which release less brake dust into the environment.
Jamie Burles, Greater Anglia managing director, said: "The Ipswich to Cambridge route is our busiest regional route.
"We were really keen to introduce longer trains on the route as soon as we could to improve our customers' journeys."
A third of the 38 Stadler trains are already in service with the rest now undergoing their final tests.
For months there have been complaints about cancellations and overcrowding on the line between Ipswich and Cambridge - with passengers often finding single-carriage trains being put on services that are already very busy.
But with four-car Stadler trains there has been a dramatic improvement in capacity.
The single-car trains are being taken out of service and returned to a leasing company. They are destined for new lives in Wales and Scotland.
Customers for Kennett: to change at Bury St Edmunds for a rail replacement service to Kennett
Customers at Kennett: use rail replacement service to Cambridge North, calling at Newmarket if required.
Customers for Dullingham travelling on the 17.47 from Cambridge, should get off the train at Newmarket at 18.07 and then catch the 18.18 service from Newmarket to Cambridge, which will stop specially at Dullingham at 18.23.
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