Parameter ‘custom_field_X’ has already been defined.
This message will appear on a Results File after an import attempt using the Account Importer tool (or one of the various update tools). “Parameter” refers to the column headers in the file you are using. This error specifically means that two headers have the exact same name. For example, you may have two columns in your spreadsheet that say “Debtor Phone”.
To fix this error, you will want to open the original spreadsheet and double-check for any duplicate header names. Using the example above, you can make it so the duplicate “Debtor Phone” headers are listed instead as: “Debtor Phone 1” and “Debtor Phone 2”
Once you have fixed the spreadsheet, you can save your changes and attempt the import (or update) again.
If you have a lot of columns in your Excel spreadsheet, you can find duplicate headers a lot faster by using Conditional Formatting. Select your header row (row 1) and click on: Home > Conditional Formatting > Highlight Cell Rules > Duplicate Values… On the pop-up window, click OK. All duplicates will be highlighted with red boxes and text.