Your problem might be the "?" and not the rest. The following works;

oWeb = createobject('InternetExplorer.Application')
oweb.AddressBar=.t.
oweb.Visible = .t.
oweb.AddressBar=.f.
oweb.Visible = .t.

>I'm using VFP7.0
>

>oWeb = createobject('InternetExplorer.Application')
>oWeb.visible = .t.
>? oWeb.ReadyState      && prints 4
>? oWeb.MenuBar         && prints T
>? oWeb.ToolBar         && prints 1
>? oWeb.AddressBar      && gets error "OLE error Code 0x80070057: The parameter is incorrect"
>

>IntelliSense shows "AddressBar" as an option, exactly like "MenuBar" and "ToolBar"
>How Can I get/set AddressBar?