The error is about a sign that is not in US-ASCII table and iconv cannot translate it.
error is at line: 40, row 531
Take a look at this sign with your favor editor, maybe it is ISO-... or someting else.
Since you will transfer from a database witch has french chars, try the following if it works.
Code:
iconf -f ISO-8859-1 -t UTF-8 < source_dump.sql > target_dump.utf8
Maybe change ISO-8859-1 to something else