Hey GregorTripper - welcome to the Ubisoft Forums! I'm sorry to hear of the issues you've been encountering with the Inside Job mission.
When you say that you're unable to use the shiv, do you mean that no prompt appears on-screen for you to select to use it? And with regard to the key, does it appear at all but you cannot pick it up, or is it not on-screen in the first place?
If you've performed any troubleshooting so far, could you please let me know the steps you've tried?