Does anybody know what this means?

[VernJensen]

Oh wait, I just realize that the *game* is giving you this error message when you attempt to open the mansion, rather than the editor. One possibility is that you set the

starting room

to a room that doesn't exist. Verify in

Mansion Options

in the editor that your starting room exists. If it doesn't, the LEVL resource is the first the game attempts to load, so it'd make sense why it wouldn't be able to find it, for a non-existant room.