If using a prefix for the drupal database, community_tasks.module will throw SQL error when creating a task

Reason (IMHO) for this are 2 bugs in community_tasks.module where db_query is called for table 'node' instead of '{node}'.
Search for 'db_query' within community_tasks.module. Wherever you find 'node' as the table name, simply replace with '{node}' (i found 2 occurences).
That worked for me, problem is gone.