Interval partitioning with restrictions: NP-complete or efficiently solvable?
Here's a reduction from 3SAT. For each of your 3SAT variables $x_0$, imagine there is one event $x_0$ and two rooms called "Room $x_0$ is true" and "Room $x_0$ is false". The event $x_0$ has to be in one of those two rooms. Whichever statement is true, that's the room we don't use. And it is going to take all day. So the only rooms generally available for other events are the rooms named with a true statement.

Now let's say you want to add a condition - $x_0$ OR $x_1$ OR NOT $x_2$. Make that into an event that's just one nanosecond long, at a random time so it doesn't conflict with the other condition-events. And it has to be held in one of "Room $x_0$ is true", "Room $x_1$ is true", or "Room $x_2$ is false".

Now solving your event assignment problem lets you solve an arbitrary 3SAT problem.