This is by design - Expression field cannot use related objects.
Hi Pavel,
But it works -:) So when i try to refer to another object, the values are retrieved. One thing: When referring to a date field in a related object, the system counts a day on the actual date. For example (with date format dd-mm-yyyy):
Object1.Date1: 11-12-2012
and when adding an expression field called date1 within object2, which has a relationship with object1 and contains the following expression:
var date1 = new Date("{!Object1.Date1}");
return date1;
Then you'll get: 12-12-2012
You can use loops, but when related records are updates we cannot guarantee that Expression will be updated as well.