Passing a variable between a parent and child package doesn't work

Has someone managed to pass successfully a variable from a parent package to a child package? I’ve tried a zillion permutations and I can’t get it to work. The strange thing was that I was able to successfully do this with pre-RTM builds. Basically, what I am trying to do is:

1. The parent package has a variable, e.g. ExecutionID which I set using a script to System::ExecutionInstanceGUID. I verified that the variable is set correctly by dumping it to a SQL Server table.
2. I created a child package variable with the same name.
3. In the child package, I’ve created a parent package configuration that points to the ExecutionID variable.
4. I am trying to read the variable in a Derived Column Task in which I have a column linked to @.ExecutionID.

This doesn’t work. Step-by-step instructions from someone who managed to concur this will be greatly appreciated.

Oh, I didn’t have any luck hitting a breakpoint in a script task inside a child package with both in and out of process execution also.

Never mind. My configuration got messed up. I am still not sure what needs to be done to debug a child packge though. Ideas?