Ah yes. That is a good question. Now I believe I have found an answer! I believe that I can convert each and every 1.24 level to 1.23 using the Overlord's patch WITHOUT EVER crashing the patched JCS! I don't think anyone has found a safe method to do so... if someone did and posted it - forgive me I didn't have time to look through the whole archives.

First of all why does JCS crash when you open a level in it? The answer is simple - the same thing that gets lost during the conversion: animated and flipped tiles showing in PARALAX SCREEN window!

So what the method?

1)Before you try to convert the level open it in a normal 1.24 JCS.
2)Delete all animations and disregard unknown tiles while saving
3)Click on Layer 8 minimize it so that no sliders are visible on the Layers part of the screen.
4)If the background on Layer 8 is too big to the shown completely after minimization make it smaller - or better completely delete it. The same with the flipped tiles - NONE can be visible anywhere!
5)Now change the tileset to e.x. Haunted House (or any that won't show up in the patched JCS!)
6)Svae the level.

7)Open the patched JCS.
8)Minimize the ANIMATIONS and PARALAX VIEW windows so nothing is visible on them! This step is very important.
9)Open the level. If you did everything correctly the JCS should NOT crash.
10)Change the tileset to one that should be used in the level.
11) Save the level.

After that the level SHOULD open in a normal 1.23.

GOOD LUCK!
Daniel.