This warning occurs when second sub attribute of a attribute is mandatory and is not specified. %s - attribute name.
Set the variable to a value.
Example
[#Menu: Gateway Of Tally]
Add: Item: "MyReport": Display: MyReport
[Report: MyReport]
Variable : MyVar:String
Set : MyVar
Use : Balance Sheet
In the above example, the set attribute of MyReport does not have the second mandatory attribute which is the value. Hence the warning, warning T0013: The mandatory second value of 'Set' is not given appears.
The code is corrected by setting the variable value.
[#Menu: Gateway Of Tally]
Add: Item: "MyReport": Display: MyReport
[Report: MyReport]
Variable : MyVar:String
Set : MyVar : "MyText"
Use : Balance Sheet