I received the same for my SSP world.Hi I just upgraded Agrarian skies server and client to v3.0.1 and get the following error message:
Forge Mod Loader had found ID mismatches Complete details are in the log file
ID 20424 from Mod Exaliquo is missing.
Any ideas.... in mean time gonna try a re-install.
cheers
Condor
AFAIK it's from a mess up last version.
Should be perfectly fine to continue and the worst would be random hammers going missing.