I have been dealing with the unable to save Secure Flight data for the past three months on a flight I am taking with my son in April.
I have tried different browsers, enter-log out-log in, clear cookies/cache, middle name/middle initial on first name line and it still doesn't work. I will call 72 hours out to try and fix, try during OLCI, and at the airport if necessary.
I chalk it up to another "not ready for primetime" web feature brought to you by the Friendly Skies IT folks.