When you export a Subscriber list from a module other than Subscriber Management, the exported file is a tab-delimited .TXT file. The Import Subscribers function requires a .TXT or .CSV file that is comma-delimited and requires fewer columns than the exported file. This article will show you how to modify the file that you obtained with the Export function so that it can properly import subscribers as well.
Important Notes:
This article uses Microsoft Excel for the instructions.
You can also complete this process with a text editor, but a spreadsheet application makes the process much easier.
Instructions
Open the .CSV file that you obtained with the Export Subscribers function
Delete the fourth column (should only be populated with OK)

Select File

Select Save As

Change the file type to CSV (Comma-delimited) (*.CSV)

Click Save

Use the .CSV file to import subscribers.
Resources
How to Export Subscribers in:
How to Import Subscribers in: