When I ride my roadie, my upper back, almost my neck area begins to hurt. It’s a muscular ache pain. Why is this and what do I need to adjust to sort it out?

Impossible to say without seeing you on it, but at a guess, you’ve got your seat too far forwards, so you are putting too much weight on to your hands in an attempt to prop yourself up.

Seat down and back, then reconsider your reach.

Don’t hunch or tense your shoulders either, drop your shoulders and let them and your arms relax. Are you new to road riding? I got back into road about 2 years ago (after 20years just on MTBs) and as Ive got used to it my bars have got lower, but if youre used to the typical MTB set up then road bike position is quite extreme and will take some getting used to. Stretching, flexibility and core strength make a real difference, your bars could be too low for you at the moment.

Crash – yes I’m new to road riding, but been on mtbs for a long time. Cricket, I did, possibly by mistake, move my seat as far forward as possible to begin with!

I had the same problem after lots of years on a mtb.
Changed the drop bars to wider ones and put a shorter stem on.
Felt to be in a far more relaxed position on the hoods but i still get shoulder ache if i try and push on too hard for too long.Probably due to tensing my body too much.You do need to get used to the road position after years on a mtb.
Without going for a comprehensive bike fit then its about experimenting.

Saddle back and down a touch.

Maybe bars up a bit too. I am chunky and returned to road riding this year and that helped me. saddle back and down allowed me to access the drops and bottoms in comfort too and put the tops in the right place too as I had been on the hoods and nothing else.

As others have said,try not to tense up. I used to get this especially in the winter months when you are cold and your muscles are tense.
Relax and let everything hang loose……well almost everything!!