Webbrowser failes on secure connection

Hey I want to make a program for my grandparents. The problem is, they don't really know a lot of internet. They have a bank account which can be accessed by the internet. So I want to make a program that automatically types in the password and account name and then surfes to the accounts bank result (or how do you call it, to see how much money you have). But my problem is that this bank (fortunately) uses a secure connection.

When I open the banks homepage in my webbrowsercontrol, and fill in the accountname and password, the webbrowser says "this page cannot be displayed" after I clicked (via code) on the submit button.

Unfortunately you can't test it because you don't have the accountnumber nor password and I will not change that :D

Any ideas why my webbroswer failes on secure connections?

Thanks
WP