It's a right pain when you have the perfect plan, and it all goes badly wrong, yes the game fails to load the ingame editor from the CAW, bang your head against wall time
But why can't you edit ingame from CAW are you ready for the horrible truth:-
You have a bad lot, the reason you can't edit ingame is that one or more of your lots is not working correctly.
Make sure you use conform edges on all your lots and your best testing ingame after each lot you place on the map, it's currently the only work around I'm aware off.
To get your current game working you going to need to delete lots, starting with the most recent lot and work your way backwards, but place a backup of your save on your desktop first, after each delete test the game, if the game loads then bingo that's the bad lot, replace the save with your backup and delete that lot in your backup and the game should load.
A tip for you is place lots in layers of 5 using the Global layer, add layer, if you have this problem again, it will help narrow down the search by deleting a layer at a time, before each test load, it will probable save you hours of testing to find the bad lot.
Not 100% sure why a lot goes bad, but the main culprit seems to be terrain adjustments, but each time you make an adjustment near a lot you should use the conform edges, it should help reduce the risk, but a test will do you no harm.
I hope this info helps somebody, I've been building all week using CAW, I've got in the habit of placing a empty lot and loading the game, my current game as got 60 lots on, I'm on my 8th backup save, each time a lot was the problem, 8 failed loads, so sooner or later, if your building a huge world, you will get hit by this bug, so you either spend 45 seconds loading in game after you place each lot or you run risk of spending many frustrating hours trying to find the culprit for a failed load.