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You need to activate the WebBrowser advanced feature for the parsing procedure to complete successfully. When these features are not enabled, the WebBrowser, in standard IE7 emulation, won't be able to complete the Document. The failure is caused by the high number of scripting errors.

I've added a class with static methods (WebBrowserAdvancedFetures) to add the required values to the Registry.
WebBrowserAdvancedFetures.ActivateWBAdvancedFeatures is called in the Form's constructor.
You can roll it back calling WebBrowserAdvancedFetures.DeactivateWBAdvancedFeatures.

How does this procedure work:

1. Instantiate a WebBrowser class (Private browser As WebBrowser). We could also use a WebBrowser control (the visible control version that a Form container can host), it's the same thing.
2. Subscribe to its DocumentCompleted event. It will be raised each time one of the HtmlDocuments inside the main WebBrowser.Document is completed. Read How to get an HtmlElement value inside Frames/IFrames? for some more details on HtmlDocuments nesting.
3. In the DocumentCompleted handler, verify that at least one of the Documents is ready to be parsed, checking that WebBrowser.ReadyState= WebBrowserReadyState.Complete
4. When it is, search for the HtmlElements that contain the data we're looking for.
5. When all data has been collected, raise an event, to notify that the parsing is completed (this also allows subscribers from other classes to be notified as well, if needed. This requires a custom EventArgs class, though) and disable further parsing of the HtmlDocument (here, this is accomplished setting a Boolean field).
6. Handle the new data (here, just a String and a DateTime objects), then reset the fields/variables used in the parsing procedure.

Remember to remove the handlers, in the Form.FormClosed event or in a custom class Dispose() method:

Managed to figure it out. Added a 2 second wait after page loads to allow loading and an error handler to identify if the required property is available.

I tried converting it using a process I know works and the file couldn't be opened in adobe reader. I used a different encoded string found elsewhere and it worked. The base64 string you have in your question is malformed.

You should use TLS1.2 as your security protocol for this site. This line should fix your problem.