The security guard is being obstructive. It's our building just go in and take it for free. We have volunteers back and forth. This is one of the reasons we left because of nonsense like this. Tell him I have authorised entry and for you to take what you want. If he doesn't let you in then he will be liable for the cost of any of the items left tell him. Tell him to get out of the way he is breaking the law by preventing our customers and volunteers access to a shop I lease.
(See why we are leaving).