A mod is incompatible
Applies to Forge, NeoForge, Fabric, Quilt.
What causes it
A mod clashes with your Minecraft version or with another mod.
How to fix it
The log names the mod. Remove or update it to a version that matches your pack.
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log