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

Not sure if this issue has been mentioned in the group, but if you
have an XML dataset and you change a column name within the raw XML,
the codebehind will not change and you will get this bogus message.
You need to do a find on the old column name in the codebehind file
and replace it with the new column name. A good way to verify that
this might be one of your issues is to use a datagrid with autogen
columns, turn off the enforcecontraints on the dataset, then look at
the header of the grid and see if any column names aren't what you
expect or if there are missing values.