Hi Rita,
You should upgrade your SQL Anywhere 16 installation to the latest support package as this is a known and fixed issue (CR #733781 in 16.0.0.1453). While the OPTION() is a good work-around for individual queries, it isn't a great resolution as you point out, since it's hard to know which queries will fail at runtime in production.
You have two options for resolution - one option is to disable intra-query parallelism everywhere, at the cost of performance:
SET OPTION PUBLIC.max_query_tasks = 1
This will take effect on all new connections, or after a database restart.
Otherwise, you can upgrade the Support Package for SQL Anywhere: ( http://scn.sap.com/docs/DOC-54706 )