I had the exact same problem as gmclelland with creating a new repeater in PW 3.0.62 for a site that had migrated from 2.x. Unfortunately, temporarily purging all of my existing repeater fields and data from the database so that I could uninstall/reinstall the Repeater fieldtype did not resolve my issue. However, here's what worked for me:
Create your repeater field using the normal method and save it to trigger the "You must assign a template to the page..." error.
Note the ID number for your new field (mine was 170)
Manually create a parent page for the repeater within the page tree (Admin > Repeaters > new) using the Admin template and the URL of for-field-170 (with the 170 being the ID from step 2) and publish it.
Note the ID number for your new repeater parent page (mine was 1949)
Using phpMyAdmin or equivalent, navigate to your Fields table and find the row for your new field (it's sorted by the same ID, so I looked for 170) and insert "parent_id":1949, (actual ID from step 4) directly after the template referenced in the Data column.
When I returned to the admin page for my field after this, the error message was gone, the details tab was present, and I could successfully add fields to my repeater.