Just tried to check-in for a BRU-LHR flight tomorrow (actually on a UA code). It appears I now have to enter API information (Didn't have to do that when flying BA on BRU-LHR a few weeks ago)

In the API, they are asking for all my names in my passport, so I entered "George Arthur Akerlof". I then got the following error message:
"Invalid passenger details entered please check the name matches the passport and retry."

It appears that this error message pops up because my tickets are booked without my middle name, i.e. as "George Akerlof".

So I removed my middle name from the API entry form, but then get the following error message:
"Unfortunately, we are unable to check you in at this time. Please check in at the airport. (1014)"

Any ideas?

No, I am not George A. Akerlof