What is the difference between SHDocVw.InternetExplorerMedium and SHDocVw.InternetExplorer?

Question

Some answers seem to suggest that I should use SHDocVw.InternetExplorerMedium to automate Internet researchers.

What is the difference between Internetexplorer and Internet Explorer?

I tried to run this code and I got an exception to throw an object

            ias.IntExpMed = New SHDocVw.InternetExplorerMedium
            ias.IntExpMed.Navigate("http://wikipedia.com")
            waitTing(1)
            ias.IntExpMed.Navigate("http://google.com")

In fact, if I go through the program, the object will be disabled immediately after

            ias.IntExpMed.Navigate("http://wikipedia.com")