As you have told you drag a HyperLink control onto your page from the toolbox. If
so, ensure the name or ID is HyperLink1. Otherwise, I would guess that
the hyperlink isn't actually on the page, since I didn't see any
codebehind instantiation of it.
As a test, try putting this before the code giving you the trouble:
Dim HyperLink1 as new HyperLink()