I found these in our watchdog log:

Unknown column 'delta' in where clause; query: UPDATE content_field_poll SET field_poll_votes = 0 WHERE nid = 12132 AND delta=0 in /public_html/sites/all/modules/pollfield/pollfield.module on line 1451.
Unknown column 'delta' in where clause; query: SELECT field_poll_votes FROM content_field_poll WHERE nid=12132 AND delta=0 in /public_html/sites/all/modules/pollfield/pollfield.module on line 1407.

That pollfield_is_delta_exist() function is not right as our content_field_poll table does not have a delta column, yet it obviously begins with 'content_field'.