To reproduce, use the SQL query page to write a query, including an OFFSET clause but no LIMIT one. The result is an error message.
The PostgreSQL documentation (http://www.postgresql.org/docs/9.1/static/queries-limit.html) strongly implies it should be possible to have an OFFSET clause but not a LIMIT one. It also notes that LIMIT NULL is equivalent to omitting the LIMIT clause - except in the ORDS, LIMIT NULL works, whereas omitting the LIMIT clause doesn't.
To reproduce, use the SQL query page to write a query, including an OFFSET clause but no LIMIT one. The result is an error message.
The PostgreSQL documentation (http://www.postgresql.org/docs/9.1/static/queries-limit.html) strongly implies it should be possible to have an OFFSET clause but not a LIMIT one. It also notes that LIMIT NULL is equivalent to omitting the LIMIT clause - except in the ORDS, LIMIT NULL works, whereas omitting the LIMIT clause doesn't.