Some guru errors are quite cryptic and hard to work out what they mean. Address Error probably means a ram issue, but I could be wrong.

It is good news that you finally got it to work. Maybe the trapdoor ram expansion wasn't seated correctly and you removing it and the putting it back in solved the problem. Long shot and a complete guess.

Other common problems like that are if the Amiga is stored in the attic and has got damp or condensation in it. So when you put it back into a warm room it won't work until it has adjusted to the atmosphere of the room.