Bump! I'm also having this issue and getting the dreaded:
We have found some problems with the details you have provided
Error during add or update contact details
... with no useful indication of what's gone wrong. I know it's pretty common, does anyone know if it's a glitch that will resolve itself, or once it's broken for a booking then that's it?
As a lowly Blue on a CW redemption I don't want to be locked out of online check in as I'd like at least some chance of a seat selection! Got a few days yet, but should I just call BA?