At a train ticket barrier what causes the machine to read "take ticket and seek assitance"?

Question

on trians in the uk

Answer 1

there are several ways, both done with sensors, one operates of weight, when a vehicle weighting so much cross over it, it will activate the machine, and the second sensor operate off of a light sensor, cross the beam and activate the machine.  or if you were to ask my grandfather he would tell you that it was a little gremlins inside the machine, and that's my it doesn't work all the time because the gremlins is always playing games with everyone

Answer 2

Most likely - a read error on the ticket.

Some tickets use a small magnetic strip to store data -and if some other magnetic source comes to close, it could corrupt the data.

Sometimes you don`t even know/realize you are too close to something.

Answer 3

I know, from experience, that London Transport ticket barriers find it difficult to 'read' the credit card sized tickets issued by mainline rail companies. Recently, when travelling from the North East to Sussex, via King's Cross Thameslink the person on the barrier at thatv station told me not to try to put my ticket through the machine, but waved me through his gate.