Whilst I recognise the need for perseverence in R.P.G. games, a difficulty has emerged of such magnitude that my patience is exhausted.

I am in the dungeon of 1,000 terrors, and have just raided the room with the three chests on the first level. In one, I found a key, labelled "stair key". When I attempted to use it on the stair door, however, nothing happened.

Please could someone tell me how to get through this door and onto the second level. I have consulted a walkthrough, which failed to solve this mysterious problem.