Xamarin - SQLite - How to get rid of mismatch exception with Guid

I continue to get an SQLite exception ... 'Mismatch' on the line sqliteConn.Insert (uniqueDeviceToAdd);

I'm trying to add a GUID to the database that I can basically use to track installs. So I want to store the GUID on the device if it doesn't have an entry in the UniqueDevice table, or retrieve it if it does.

I have tried storing the Guid as a string and using .ToString() but I still get the same error.

Thanks...

string folder = System.Environment.GetFolderPath (System.Environment.SpecialFolder.Personal);
        var sqliteConn = new SQLiteConnection (System.IO.Path.Combine (folder, "TEST.db"));
        Guid uniqueId;
        if (sqliteConn.Table<UniqueDevice> ().Count() == 0) {
            uniqueId = Guid.NewGuid();
            var uniqueDeviceToAdd = new UniqueDevice {
                UniqueDeviceID = uniqueId
            };
            sqliteConn.Insert (uniqueDeviceToAdd);
        } else {
            uniqueId = sqliteConn.Table<UniqueDevice> ().FirstOrDefault ().UniqueDeviceID;
        }




public class UniqueDevice
{
    [PrimaryKey]
    public Guid UniqueDeviceID { get; set; }
}

I've also tried totally deleting the tables etc. to no avail