I noticed that someone searched for these terms.
This is probably going to be short and sweet:
business objects operator "????"
Whenever you find ???? inside a variable, it simply means that the object that was used
to create this particular variable, is no longer in the query.
Let's say that you create a variable Year. And you use the following formula:
and then, remove the object [Sales date] from your query.
The object Year will then contain =year(????)
Not good :)