hi everyone!

Please help me with this...I'm trying to create a relation (master/detail) and got a code from MSDN. When I ran the program, this error appeared:

An unhandled exception of type 'System.NullReferenceException' occurred in Quote.exe

Additional information: Object reference not set to an instance of an object.

This highlights my code in declaring the relationship...
ds.Relations.Add("DocTran", ds.Tables!Qoutedoc.Columns!Reference, ds.Tables!QuoteTran.Columns!Reference)

What's wrong with my code? What did i miss out? Please help me! Thanks in advance.