Вот, что нам говорит help Excel:


The properties of the Err object are set by the generator of an error — Visual Basic, an object, or the programmer.

The default property of the Err object is Number. Because the default property can be represented by the object name Err, earlier code written using the Err function or Err statement doesn't have to be modified.

When a run-time error occurs, the properties of the Err object are filled with information that uniquely identifies the error and information that can be used to handle it. To generate a run-time error in your code, use the Raise method.

The Err object's properties are reset to zero or zero-length strings ("") after an Exit Sub, Exit Function, Exit Property or Resume Next statement within an error-handling routine. Using any form of the Resume statement outside of an error-handling routine will not reset the Err object's properties. The Clear method can be used to explicitly reset Err.

Use the Raise method, rather than the Error statement, to generate run-time errors for system errors and class modules. Using the Raise method in other code depends on the richness of the information you want to return.

The Err object is an intrinsic object with global scope. There is no need to create an instance of it in your code