Why, following the enabling of Knowledge Advanced, are my production answer pages broken?

Environment:

Customer Portal framework versions 3.2.x and earlier, Knowledge Advanced implementation

Issue:

Answer pages (such as /app/answers/detail/a_id/xxxx) return a blank page with the error message "There has been an error with your request."

Resolution:

When Knowledge Advanced (KA) is first enabled on an existing site, it is common for Knowledge Foundation (KF, i.e. legacy) answers to still be enabled so that they can be viewed in production while implementation work is being completed for the migration. In this case, the production customer portal would still display KF answers while development mode is being updated to display KA content prior to staging and promotion.

Since Knowledge Advanced is only supported on Customer Portal frameworks 3.3 and higher, the logic for handling this case is not in place on lower versions. Prior to enabling KA, you will need to be using 3.3 or newer in production or Knowledge Foundation answers will immediately stop displaying once KA is enabled.

Please review the answers Customer Portal Migrations and Upgrading Customer Portal Framework from v3.2 to v3.3 as they may be useful in this case.