Like some other posters on this discussion area, I am only just coming back. I am trying to get Forestry (forestry_1.11.2-220.127.116.11.jar from https://minecraft.curseforge.com/projects/forestry/files) working for 1.11.2. I installed Forge just fine. If I run the game without Forestry in the mods folders, it runs with no issue.
However, as soon as I put the jar in the mods folder, I get the error below
What am I doing wrong? Do I just have the wrong download? Is there even a Forestry download for 1.11.2?
You probably only installed the "recommended" build of Forge (2228), but according to that image, Forestry needs a slightly newer build of Forge than that (2230). Try using the "latest" build of Forge instead.