Oh ok sorry I was not sure which method you used.
In that case, make sure your Cast To node is the name of your HUD blueprint, like this:
It works correctly for me here, when you drag the blue wire off of Get Hud and are looking for the Cast To node, make sure you have Context Sensitive enabled, there is an issue in version 4.5 that causes it to disappear with that option turned off (fixed in 4.6 though).