When importing participants it is possible to receive an error message if something in your import file is incorrect. Below is a list of possible error messages with explanations and possible fixes.

Unknown column

A column in your Excel file does not exist as a data field in your event file. You should change the column name in the Excel file to match the data field in your event file. If the data field doesn't exist, you can create a custom field in Main Window > Participants Data > Additional Fields.
Check your import file for hidden columns. In Excel, it is possible to hide columns from view. When importing these columns are still visible. Look at the column lettering and see if a letter is missing. This will indicate a hidden column.
Check the spelling of the column name in your import file to make sure it matches the field you are trying to import.
ADVANCED. Check the box labeled "Automatically create additional fields for unknown columns". This will generate additional fields for any unknown columns - but you should check that you do not have an error in an existing column name before using this option.

File contains more than one participant assigned to Bib 100, which is not allowed. Please correct this problem and import again.

This indicates you have more than one of the same bib numbers in the Bib column.
In your Excel file, check the Bib column for duplicates. It helps to sort your file by the Bib value.

Error: Invalid col name: My Data

This error indicates a column name that is invalid.
Column names cannot contain spaces or special characters.

Bib Existing

This error happens when you are trying to import a list of participants and mapping on a value other than Bib.
This error indicates that one of the participants being imported has a Bib value that already exists in the event file and the mapping value does not line up.
For example, Bib 100 exists in the event file with a mapping value of 1. You try to import bib 100 under a mapping value of 2. Bib Existing error will be thrown.