Access VBA sign into web URL

[PhilS]

Trying to get some VBA code I found here to work and am not having any luck. I get "Run Time Error 91 - Object variable or with block variable not set"
[...]
.Document.all.Item("loginUserName").Value = "username"
.Document.all.Item("loginUserPassword").Value = "password"

The web page does not contain any element named "loginUserName".