If the viewports are there, open the log and tell us what package it says it can't find.
What's in the log?
If it's broken actors, you'd see SOMETHING in the log telling you it couldn't load X class in Y package or something along those lines. It sounds like your entire map was deleted and then saved over. How big is the .unr file? You can try opening the .unr file in Notepad, saving it as a .t3d, and reimporting it, but I'm not sure if that will work. I know most data is stored in basically a text-like format for .t3ds and .unrs are similar, but not quite the same.
Please post your editor.log contents on pastebin and link to it here. I've gotten this error before and it's always been a failure to load some content.
Hey. I'd love to help you but... we need THE LOG
or the file itself.http://pastebin.org/#stopbeinglazyweWANTtohelpyou