Most Immersive Engineering problems fall into two groups: the game cannot load the mod correctly, or the game loads but a machine or network is configured incorrectly.
Startup crash after adding the JAR
Check that the game is Minecraft 1.21.1 and the loader is a compatible NeoForge 21.1 release. Then look for duplicate JARs and read the first dependency error in the log.
Mod missing from the loaded list
The file may be in a different profile’s mods folder. Multi-instance launchers commonly separate each profile, so confirm the actual game directory for the profile you launched.
Multiblock will not form
Compare the block pattern and orientation carefully, then verify any required interaction tool. A single wrong block or rotated structure can prevent formation.
Wire connection fails
Check connector type, wire type, endpoint validity and distance. Rebuild the shortest possible test connection first, then expand the route once the basic link works.
Next step
Once your setup is stable, use the other guides on this site to plan power, wiring, performance and larger factory systems. For the file itself, use the main direct download section on the homepage.