This message appears when you are creating a property checkpoint. TestComplete displays it if you selected some property that cannot be validated by this checkpoint, for instance, a property that returns an object.
Property checkpoints can work only with properties and fields of simple data types: string, integer, floating-point, boolean (true or false), date/time. They do not support properties that return object references or arrays.
To verify complex data, you have to create custom verification procedures in your tests. These procedures will retrieve all the desired values from objects and check them against some expected value.