Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.

Well, this was a fun error I received today, and after banging my head against a brick wall, the solution was simple.

The typed dataset that I had created in Visual Studio, was not a direct match to the table that I was accessing on the development SQL DB. I updated the dataset, and hey-presto, we are all fine again now.