Subject column header shows red warning triangle
This is usually displayed for 2 reasons;
You already have a subject in your database with the same name but mapped to a different qualification
You already have a subject in your database mapped to the same qualification but named something different
In either case, you can proceed with the import as this is only a warning that you are potentially about to create a duplicate subject. This can be fixed later on using Admin > Edit Subjects if required.
It is possible that the warning triangle will remain even after making the necessary changes in the import, in which case it can also be ignored.