Uploading error from very small test mysql.sql dump file

greetings, i'm just trying to get started with this stuff. each step
seems to be an uphill battle, but i'm finally at a point where i can
attempt to create some sql data in Google Cloud SQL...and alas,
another wall.

i have a very small mysql dump file called videopostcard.sql in my
bucket called gs://mhs. i've tried and failed to upload several
larger dump files but this file is very small and simple, yet still
throws same log error upon upload attempt via Actions->Import button
on GCSql page. Successfully followed all of these instructions:
https://developers.google.com/cloud-sql/docs/import_export#migrate

the log always shows something like:
Failed to import gs://mhs/videopostcard.sql: An unknown problem
occurred (ERROR_RDBMS)