what MrJack said. Also, try rotating the triggerbox 180 degrees. sometimes they have to be facing a certain way. I've had that happen to me and by rotating it, it worked. Also, if it's against a wall, make sure it sticks out far enough. there may be collision on the wall that you can't see, but covers your box preventing you from activating it.
edit: also be sure to give your trigger a name. they don't become click-able unless the box under the name tag is filled in.
if you're not sure how, to fill in the object property and have it point to your actual container, double-click the script while in the trigger panel.
a list of properties comes up. Edit the field and select your container from the drop-down list or choose the option to click the object in the render window. click anywhere and hit okay to save that.
These are just a run-down of things as to why it may not be working. Again though, once you do it a few times and get the hang of it. it's really simple and making trigger containers becomes a snap.

Good luck.