SqlCeDataReader will not return any records when using a string value in the
Where clause.  Integers work fine.   Following is a example of the problem

// Database columns            
//------------------
// ID (int)
// SizeId (int)
// LookupCode nvarchar(16)            
// TestCode nchar(16)

// The following three records are in the database
//------------------------------------------------
// ID   SizeID  LookupCode     TestCode
//  1    100     123456              123456          
//  2    200     7890              7890            
//  3    300     333333333333 333333333333    

SqlCeConnection _conn = null;

string _dataSource = "Data Source = \\Program Files\\SQLtest\\TestDB.Sdf\\;";
_conn = new SqlCeConnection(_dataSource);
_conn.Open();
           
// Only the last Select statement works.  
// The first 3 does not return any records            
//
// string _sql = "Select * from UPC where LookupCode='7890'";
// string _sql = "Select * from UPC where LookupCode=N'7890'";
// string _sql = "Select * from UPC where TestCode=N'7890'";

string _sql = "Select * from UPC where SizeId=200";

SqlCeCommand _cmd = _conn.CreateCommand();
SqlCeDataReader _rdr;
_cmd.CommandText = _sql;
_cmd.CommandType = CommandType.Text;
_rdr = _cmd.ExecuteReader();
while (_rdr.Read())
{
   txt2.Text = _rdr["ID"].ToString() + " " + _rdr["SizeId"].ToString() + "
" + _rdr["TestCode"].ToString();
}