Scripts for beginners.

1) MessageBoxes cannot be script-configured for anything other than the main text. For more interesting things, it's better to use TalkBoxForPlayers (since version 3.1), described in Jack_of_Shadows' FAQ.

2) All objects are stored in the objects list in map.xdb. Using a text editor, find there objects with negative coordinates (or exceeding the map size) and delete the corresponding block of the form <Item>...<Item/>. If you know the path to the object's Shared, you can search by it.