I've written an Add-in in Excel VBA. I'm made a function to check for updates. It uses ie, and looks something like this:

Public Sub UpdateCheck()
    Dim ie As Object
    Set ie = CreateObject("internetexplorer.application")
    ie.Visible = False
    ie.navigate "https://example.com/checkforupdate"

    Do While ie.readystate <> 4: DoEvents: Loop

    Set HTML = ie.document
    If HTML.DocumentElement.innerHTML = "update is available" Then
        MsgBox "An update is ready. Go get it!"
    End If
End Sub
Now I can test that out by running it manually from the Macro dialog. It works great!

My problem is, that I want this sub to run automatically whenever Excel runs. I've tried calling it from "Workbook_Open()" in my add-in, but I found that calling it from there prevents the workbook from opening fully. Excel just displays a grey screen. Not sure what's wrong.

Anyway, when should my update sub get called?

Thanks!