Another virgin online check in question...

[Kraken]

When Virgin OLCI "coughs" on your outbound flight from the UK, it's normally because one [or more] of your party have been SSSS'd. (Selected for Secondary Security Screening - i.e. a thorough search of your hand luggage just before you board).

The OLCI system should check you all in, but it will refuse to issue boarding passes for the members of your party that have been SSSS'd. No idea why, as it's the barcode on the pass that matters & it is the same if you print it at home or collect at the airport. The main difference is an airport issued boarding pass will have SSSS printed in the bottom-right hand corner (possibly just in case the barcode does not scan).

Your seat selection should be locked-down (subject to operational changes) even if the website won't issue a boarding pass.

You only get SSSS on flights to the USA - as the USA deem any foreign country to be inherently dangerous & have done for years, even 10+ years before 9/11. The questions we used to get about our luggage at Manchester in the early 1990's before AA check-in were bizarre. Yet on the return journey you just drop the bags at check-in "no questions asked" and then pass through US airport security - which was a joke before 9/11 and now the TSA have taken over... well let's not go there!