You may be logged into a vault but the program is not, and you haven't told it which vault to use. Even if you only have one you still have to tell it to login and the name of your vault, but if you are already logged in it won't ask for the user/pass. Try this:
Dim vault As IEdmVault5
vault = New EdmVault5
Dim tt As Boolean
tt = vault.IsLoggedIn
Sorry, just saw the next few lines about the vault combobox, that login line should be:
You may be logged in, but is your program?
You need to call LoginAuto() or Login() before checking IsLoggedIn.