Our company is not currently using Vault, so I'm not that familiar with it. All I can do in this situation is make educated guesses, based on previous similar situations, without being able to test my theories on my local PC. So, I may not be much more help on this issue.
All I know is that I have used both of the codes I posted earlier for other similar situations, and they worked for those situations. The SendKeys method is often a 'last resort' method, because it can be a little unstable/unpredictable. In some situations, when I use that method, I had to precede that line of code with another like the following, before it would work.
AppActivate(ThisApplication.Caption)
System.Windows.Forms.SendKeys.SendWait("{ENTER}")
That extra preceding line, as I understood it, was used to return system 'focus' back to the main Inventor application's window, from wherever it was, so that the SendKeys signal was being sent to the correct target. It's a little complicated, so below I have a couple of links to Microsoft's pages for these methods.
SendKeys Class
Interaction.AppActivate Method
(Don't forget to click on the little drop-down list near the top right corner of these webpages and change C# to VB, to the examples will change to vb.net examples.)
Good luck.
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Wesley Crihfield

(Not an Autodesk Employee)