If you are having problems with installing worlds since the 1.42 patch (Seasons) then you are not alone.
It seems that there is a bug either with CAW or perhaps the Launcher, so that the world files do not get installed correctly.
This is what I found:
-If I open a previously created world and edit it, I can export the world and install it.
-If I open a previously made world and add a festival lot from the library, I can export it but Launcher will not install it.
-If I create a new world, I can export it but Launcher will not install it, even if it has no festival lot.
The only workaround I have found for this is to do the following:
1) Install the world through Launcher.
2) Open your DCBackup folder. Sort it by date, find the LARGEST file with today's date, and right click>Copy.
3) Go to [Game Install Location]\Electronic Arts\The Sims 3\GameData\Shared\NonPackaged\Worlds and paste the file there. It is a .package file, so you will need to rename it to [worldname].world, where [worldname] is the name of your world. You need to tell your computer to show file extensions if it does not already. You may have to give administrator access in order to rename the file.
4) Open The Sims 3, and the world will now be in the drop down list to play.
Note: the only way to uninstall these worlds is to manually delete the file from [Game Install Location]\Electronic Arts\The Sims 3\GameData\Shared\NonPackaged\Worlds; you should be careful to not delete any other files (especially Sunsetvalley!). You should be sure to delete all worlds installed this way once the Launcher/CAW is fixed, and install them the correct way.
Note: If your world has custom content packaged with it in the Sims3Pack file, this method may not work. As long as you remove your DCBackup folder before exporting the world, this should work.
If you are having an error when you save in CAW, which says it saved with errors and that lot files are read-only, then try saving your world as another name. It seems that CAW is either not releasing the file lock on those lots, or perhaps there is an error with the files themselves. So click file>save as and give it a new name.
Note: be sure not to use any punctuation or non-alphanumeric characters. Otherwise you will have problems playing the world (saves will not re-open). So myworldV1.world is okay, but myworldV-1.world is not.
If you still have errors or cannot use CAW after trying all of the above, test without custom content, and also clear your game caches and CAW caches. Details here: http://modthesims.info/showthread.php?t=441595
Also test with a brand new world in case you haven't already.
Hopefully this will help someone, as I am able to use CAW 1.18.5 without error or crashing, although I do have to manually install worlds as described above.