I have followed the instructions on the spongeforge server installation page. I do have islandcraft installed and I did change the line to:

world-generation-modifiers=[
"islandcraft:biomes"
]

and still i keep getting the message: World generator modifier with id islandcraft:biomes not found. Missing plugin?

my server log:
2017-03-01-7.log.gz

thank you

my fml:
fml-server-3.txt

I also tried it with voidcraft, but the same error message appeared: World generator modifier with id islandcraft:biomes not found. Missing plugin?

Which version of Sponge are you using? I haven't updated the Sponge version since Sponge 3, I think? Things have changed since then... I need to look into it.

1.10.2-2221-5.2.0-BETA-2219, this is the version of sponge I use. I wish you luck in fixing it.