Try changing it to a text field instead of a date field.
What is the name of the field with the first calculation? Document Date or Destroy from Office? I'd guess Destroy From Office, but I'm not sure here.
You have a syntax problem that is needlessly complicating things.
In the first expression, you can use: Date ( 0 ; 0 ; 7 ) ; Date ( 0 ; 0 ; 1000 )
and get the same results, but I doubt that you want the values these will return as these will be dates that are centuries in the past. What value do you want returned by this calculation? And what return type have you selected for this calculation? Number or Date?
In the second expression, you will get the same results if you use:
Document Date + Destroy From Office
Please note that in both your original expression and this much simpler version, both fields must be of type date ( or a calculation with Date as its Return type) in order for the calculation to work.
Would I be correct that you have a whole series of heading and category codes for your document records? and each has their own data for how long they should be retained, when to destroy or move etc?
If so, I'd create a table of this information instead of using calculation fields. This makes it easier for a non database developer to update and modify this information as needed without having to make a bunch of changes to different calculation fields. Instead, your database can use relationships to compute and copy these dates into each new document record by looking up data from this table. (This would be much like an invoice system where entering a product's ID code looks up it's unit price which is then used to compute the total cost for a specified quantity of that item--only with a date as the result instead of a cost value.