I don't think I have ever come across a commercial service that has proved so difficult to join. I have never been a member of Gold Circle or had an account ported. I am an Avios.com and BAEC member, but I've tried using different email addresses and on each occasion get the vague message:

Unfortunately we are unable to complete your registration.

With no clue as to what I am supposed to correct.

I've followed all the helpful suggestions #16 and tried variations.

Think I'll give up and just avoid Aer Lingus generally.