Hi ,
I was able to reproduce the crash and find its source! There seems to be far too many particle systems in play for a system to handle. This is putting too much strain on the cpu and causing it to crash. If you take your map out of your project, put it into another project and remove a large portion of your emitters (I removed all but one of each to test) you should be able to convert your project without problem after that. The maximum particles you can have in one scene at a time is 1 million before the editor crashes. There are two things you can do to get the effect you are looking for, however. 1. create switches to turn particle systems on/off based on distance/sight so you are not rendering all of them at once. 2. Remove many of them and place a specific particle system set around the player or camera that follows them and goes out enough distance to prevent the player from seeing that it is a cylinder around them. You can have a few additional particle systems to give the effects you want or to convey distance, but the bulk of the work will be done by the one or two that follow the player, which frees up a significant amount of processing power for other tasks and won’t crash the editor. Once you remove the particle systems, save the map and re-add it to your project, then try to convert in place. This should allow you to continue moving forward with your project.