Fill Combobox With Database Query?

I am having a problem with filling a combobox with unique values.Im not very good at vb either so I will explain what I have done so far.

1. I added a combobox to my form called Combobox1

2. I clicked the little triangle widget thing on the ComboBox1 set the dataset to MyDATASETDataSet1

3. Display Member: CurrencyCountry, Value Member: FCode, Selected Value = None

4. I fill MyDATASETDataSet1 when the form loads using:

PricesTableAdapter.ComboBoxQuery(CurrencY_DATABASEDataSet1.Prices)
ComboBoxQuery =
SELECT DISTINCT [CurrencyCountry], [FCode] FROM [Prices]

The form does not load, i get the error: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.If I replace ComboQuery with Fill Query (which is the default fill command) it displays results....but not unique results, i see the same items being repeated throughout the list in the combobox.I guess my questions are:

1. when you fill a dataset do you need to select all the fields when you are creating your query?

2. if i simply wanted to perform the following lookup:

SELECT DISTINCT [CurrencyCountry], [FCode] FROM [Prices]and set the combobox Display Member: CurrencyCountry, Value Member: FCode how would I do this in the code?

3. how can i change my query to display only unique values, distinct doesnt seem to be working?