Can anybody tell me why when I put my tickets through a ticket barrier it pretty much always denies me entry and tells me to seek attention? I buy tickets online and collect from a ticket machine. I also have a railcard. It gets a bit infuriating, especially if the train is tight and staff are not that close or dealing with other passengers.
There are many reasons a ticket can be rejected,
1. The magstripe may have never been written properly in the first place.
2. The magstripe may have become demagnetised. A lot of phones seem to have pretty strong magnets in them now and I understand these can demagnetise tickets.
3. Some gate-lines reject all railcard tickets, theoretically so staff can check the railcards though whether they actually do is another matter.
4. Some gate-lines have over-simplified peak/off-peak rules.
5. More unusual tickets may simply not be recognised by the gate at all. This is particularly an issue with rovers or when breaking your journey.
There is a 2 digit "reason code" displayed when the ticket is rejected, if you can see what that code is then it may give more clues as to what is going on.
Also my understanding is that on many gates the logic for e-tickets is completely seperate from that for magstripes. So if e-tickets are available for your journey it may be worth trying them.