I see there are quite a few posts concerning email accounts missing from the list under the master BT ID, looking through these post my impression is that the answer is generally that it is due to migration from BT Yahoo. My problem is similar to these however I do not think it is related to the migration.
As per the similar threads I am missing 2 email addresses from the list under my account holder BT ID. However I do not think this is due to migrating to the new system as only one of the missing accounts has been transferred to the new system and one of the addresses that is on the list has already been migrated to the new system.
The email accounts can be accessed from webmail normally.
I have tried re-associating them from the BT ID, however everytime I tried to access this page I get the same error message:
Warning Sorry, because of a technical error we're not able to continue at the moment. Please try again later.
I am assuming that although some of the addresses are listed as btinternet instead of btopenworld is not an issue as they are equivalent.