Csv importer unique columns

Hello,
I am trying to import a file using the csv importer. I receive the following error message.
"Your file is incorrectly formatted. Header row contains 19 unique column name(s) for 20 columns. Please ensure that all column names are unique."
The column headers are the following:
Contributor
Type
Provenance
Creator
Bibliographic Citation
Coverage
Date
Identifier
Accrual Method
Source
Title
Alternative title
Accrual Periodicity
Subject_1
Subject_2
Spatial_Coverage_1
Spatial_Coverage_2
Spatial_Coverage_3

I was hoping to map multiple values to elements, e.g. Subject_1,
Subject_2 as two inputs of the element Subject.
I would be grateful for any suggestions

That error generally means that there are more columns of data than there are columns for headings. One reason for that could be a malformed CSV file due to a comma appearing in one of the fields. The application you are using to export the CSV might have an option to make the export 'safer' by adding quotes or escaping commas in the text.

Of course, it's also possible that there's just a missing heading.

From what I can see, one of those two is the likely culprit.

I double checked and there is no missing heading. Therefore I will try to "make the export 'safer' as you suggested. Thanks for the help.

I deleted three columns whose contents I had cleared some time ago and I resolved this issue. Nevertheless the csv file is not imported and I do not receive another error message. Any ideas?

If something went wrong, the status of the import should be listed as "Error" in the list of imports. If that's the case, there should be some debugging info in the application/logs/errors.log file.