While starting the modpack SuperSymmetry on the latest version:
crash-2021-11-06_20.21.35-client.txt
It appears to be an incompatibility with a class from the mod Trinity.

This is an issue with Trinity, not ICBM-Classic. A file got removed in ICBM which Trinity apparently uses, and it's the Trinity author's job to update their mod to support the new ICBM version that does not contain this file.

I don't recall what that file was but I suspect it is now named icbm.classic.api.refs.ICBMExplosives