Declare and use range in vba

You are discovering Variant and object references.

A Range is an object - a Variant can be anything including an object.

This is the correct way to go about it:

Dim rg As Range     
Set rg = ActiveSheet.Range("A1:B2")  

Because:

1. You're explicitly declaring rg as being a Range object.
2. You're correctly assigning the object reference with the Set keyword.

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If you don't specity the Set keyword, you're assigning an object reference using the VBA syntax for values assignments, and that's an error:

rg = ActiveSheet.Range("A1:B2") 

If you declare multiple variables in the same instruction, and only specify a type for the last one, then rg is a Variant here:

Dim rg,rg2 As Range  ' this is like doing Dim rg As Variant, rg2 As Range
rg = ActiveSheet.Range("A1:B2")  

And VBA will happily let you assign a Variant with just about anything... but things will blow up at run-time.

Expanding on Mathieu Guidon's answer:

If you want to specify two objects in the same instruction (one line), you should use the following syntax:

Dim rg as Range, rg2 As Range

This will correctly assign both rg and rg2 as a range object.

Using Dim rg, rg2 As Range, only rg2 is assigned as a range object (rg becomes a Variant), as Mathieu Guidon correctly explains.