Check in problem - BA115
 

Yes, it does. Assuming that all your advance passenger information is up-to-date and you have a ticket number (use CheckMyTrip), secondary screening is the most likely explanation.

The flight is full, but they are still selling F seats (so lots of upgrades likely, denied boarding much less so):

F2 A2
J2 C0 D0 R0 I0
W0 E0 T0
Y3 B0 H0 K0 M0 L0 V0 S0 N0 Q0 O0 G0

Just get to the airport early (3h before if you can) and all should be fine.

While there are multiple entirely benign explanations, not the least of which is secondary security screening required, some reasons are not benign.

For that reason, it make sense to call BA and ask. If it is secondary security, you will get some slightly silly answer because BA can't tell you that in advance. If it is something else benign, you will know what it is or fix it. But, if there is a problem with the ticket for any reason, best to get it fixed from the comfort of home. Not only no need to hang around airport counters, but also hard to predict whether you need an extra 1, 2, or more hours.

Not being able to check-in DOES NOT automatically mean you have been selected for additional security screening. People need to stop immediatly jumping at that reason.

I have been unable to do OLCI several times and not once was it because of SSSS.

Most people who get SSSS are able to do OLCI but can't print/generate their Boarding Pass - which is not the issue here.

The most common reason is the passport / visa check followed by minor ticket issues. Other people have reported (and am not saying this to get the OPs hopes up) that it was because they had been given an op-up

There is a comprehensive thread about the reasons in the dashboard.

I have had this twice:
1) 'Plane was smaller than originally intended and when I got to the airport it was "£400 for volunteers for waiting until next day"
2) Business Class was overbooked - ironically the first time I had paid my own cash for Business Class. I was offered a downgrade to WT, which I declined. I flew a day later, and was upgraded to First at the gate.

So expect some problem, and prepare your helpful bargaining replies, E.g. "We are happy to go via BOS/PHL etc if upgraded", "We are happy to fly AA if upgraded", "We will accept compensation of £xxx if delayed a day" etc.