Unhandled error messages from `convert_to_der_and_cache` method when invoked

Error messages handled and returned from method `convert_to_der_and_cache` is not consumed properly when method is actually getting called. Need to have error messages updated when calling `convert_to_der_and_cache`

Locate convert_to_der_and_cache and every call site, then trace how its returned error messages are consumed. Confirm the expected error wording and handling from nearby code or existing tests; done means errors returned by the method are correctly consumed and the messages are updated when it is called.

Written by the indexing model from the issue text.