The foreach loop container tutorial from chapter 4 doesn't work as described. It seems that Dts.Variables is always empty no matter what I try to assign on the Variable Mappings page of the Foreach Loop Editor. The error is "Object reference not set to an instance of an object", which happens when I try to reference variables("FileName"). I would like to download the example code but it seems there is none for chapter 4.

if you mean the foreach loop with excel example in chapter five, here is what i did to make the example work.
on page 139, when you create the <new variable> "ExtractFileName", make sure you assign a value to the variable (i.e c:\folder\filename.xls).

also, on page 140, connectionstring is wrong. you should select excelfilepath and assign it to your variable. click evaluate expression and you'll see the value you assigned to on page 139.