I've just tried to post some pictures of various routes and dates and the same error message but until I have posted 5 posts, I can't post the pics!

The examples were LHR->HEL in January, HEL->MAN in Feb and ICN->HEL in March, all with the same error text:
"Sorry, there’s a problem with booking this journey online. You can try selecting other flights or contact us so an agent can help you book the flights you have selected"
"Total Price (Including all taxes, fees, and carrier charges)
Sorry there is a problem with booking this journey online. Try selecting other flights"