Hi,
I'm not sure if this is a problem of MultiMc or Forge but when I start a new instance in MM and start it before installing Forge it works (so no mods just vanilla). But when I instal Forge (tried 4.1.1.251 and 4.1.1.297 as i beleve it is the latest) it gives an error and shuts down. The log file should be in the attachments.
Thanks for looking at this post.