Cancel the Import routine and review the import file for duplicate column headers.

When duplicate column headers exist, the import will fail to return to the user back to the Data Import menu. Remove or rename any duplicate column headers and try the import again. 

If the issue persists or there are no duplicate column headers, try the following steps:

1. Select File > Save As and save a new copy of the file. Then try the import again.
2. Copy the data from the file into a new .CSV file. Try the import again.