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The error message is pretty much self explanatory.
There is no entry in the cvff force field - at least the version
bundled with msi2lmp - for an atom type c3'
so you must have either typed your molecule/system for a different
force field, or were using a different version of cvff.
msi2lmp cannot work correctly with such inconsistencies, and thus
aborts. this is all a user error, not a fault of msi2lmp.
axel.