It’s an eStore plugin, also not a new installation nor a change of hosting provider. I tested it as per your link above and it was a PHP session issue so I contacted my hosting provider and passed on your instructions as to how configure the session save path correctly. They did so, and now it seems to be working perfectly again. Thanks so much – I had been trying to fix this myself for ages and just ended up more and more confused, you did it so easily! Next time I have problems I’ll come here first. Thanks.