I have many-to-one mappings working fine, but a one-to-many relationship between locations and location_times keeps giving me an error.
I keep getting this error: <
This is usually a problem of ID name mis-matches on your tables. Check to ensure that Location has an ID column on the table and that it follows your convention or is mapped correctly. You don't share Location's map, full object graph, or any of the tables so its hard to tell what the IDs are named and if they are matching up correctly.
Edit:
Per RichardD's answer in the comments, modify the LocationMap to be as follows:
public class LocationMap : ClassMap<Location>
{
public LocationMap()
{
Table("Locations");
Id(x => x.locationID).Column("ID");
HasMany(x => x.LocationTimes).KeyColumn("LID").Inverse().Cascade.All();