I opened and ran Dota 2 earlier today with no issues. Now I'm getting this error.
It means that the virtual method
InstallSchemaClassBinding of one of the schema bindings from
libschemasystem.dylib has a registration error because of a local class not locally-scoped.
Although you didn't ask for a fix, I would suggest a clean reinstall.
To fix this manually, you'd need to bypass the anti-data tampering code, which I would not recommend if you do not have RE experience.