When uploading a file through Browser Import in Classification Importer, a warning can be seen sometimes - "the key on line has too many columns".
This warning is generated by the invalid number of columns in the Classification file. For example, there are 2 classifications of a variable and the file trying to be imported contains 3 columns against the key column. This throws a warning while uploading the file in the Classification Importer tool.
To resolve this, validate the number of classifications of the variable and then ensure that the number of columns matches with the variable classification. The file uploaded with the same number of columns (other than key column) as the number of classifications of a variable would be successful without any warnings.