If the Excel application is not available for import and export with an Excel connection, Excel worksheets can be imported and exported using an ADOdb connection. This is the standard situation when working with Enterprise Studio Online. In case of an on-premise installation of Enterprise Studio, ADOdb has been installed for this.
If you are importing table column headings from Excel with an Excel connection using ADOdb (instead of Excel), it can happen that not all column headings are imported. This is caused by the fact that the ADOdb connection does not accept it when the type of the heading (text in most cases) does not match the type of the cells below the heading containing the values (for example numbers).
To solve this problem, create an Excel file with just the headings, and use that file for importing the headings. All headings will be added to the Excel table mapping in Enterprise Studio. After that you can complete your table mapping, and import the values using your original Excel file.