Go to the SuperLemmix Editor Release Topic (https://www.lemmingsforums.net/index.php?msg=105112) to get the latest version of the SLX Editor, recommended for use with NeoLemmix CE.
TIP: To use the SuperLemmix Editor with NeoLemmix CE, go to Options and choose "NeoLemmix" or "Auto" as the Editor Mode. This will set all controls to NeoLemmix-only.
Please note: If you are using this editor to make NeoLemmix levels, make sure you are using it alongside the NeoLemmix styles, not the SuperLemmix styles, and vice versa. You may encounter issues such as incorrect exit positions, incompatible water object types, etc. if using styles from the other engine.