There are two problems here a use you haven't met one of them yet, because the other prevents it occurring.
The problem you have met is simple: you cannot access class instance fields, properties, methods, or events within a Shared method because it (by definition) does not have an instance associated with it.
That is what the error is saying: a Shared method does not have any interface to work with.
You may be able to get round this by removing the Shared attribute from the method.
The problem it "hides" is that you cannot access UI controls from a thread other than the UI thread it was created on - and if you try you will get an error at run time: a "cross thread exception".
To cure that, you will be Invoke the control to move the update back to the UI thread:
Control.Invoke Method (Delegate) (System.Windows.Forms)[
^]