The source of this error is due to a column header exceeding the recommended byte length in the CSV file. Any column headers that contain a large number of spaces or characters will result in exceeding the maximum byte length. When adding a space to a column header in your CSV file, NetCommunity will generate an underscore automatically as a result.

To resolve, edit the CSV file and adjust the name of the column header referenced in the error. Once the header has been adjusted, save the CSV file and attempt to upload again. 

Example: 

Original: MY________EMAIL______COLUMN_______HEADER__________IMPORT

Adjusted: MY_EMAIL_COLUMN_HEADER_IMPORT