VLookUp

hello,

I run this code:

Excel.Range rng = (Excel.Range)custWS.get_Range("A1", "B" + custWS.UsedRange.Rows.Count.ToString());

exObj.WorksheetFunction.VLookup(((Excel.Range)sourceWS.Cells[i,1]).Value2.ToString(), rng, 2, false);

and I get this error:

VLookup method of WorksheetFunction class failed

please help me understand what is the problem

thanks