Hi smhoon
Version 6.8B is very old, and like Andrew says it may be a bug that existed in that version.
But there is a much better way to handle what you are trying to do, using the function Maintenance | Update Archive Batches. I think that function exists in version 6.8B. It also assumes you are not using the Text Block in the Ship to/Text tab on your invoices already.
First create a text code under Edit | Text Maintenance, and enter the description there.
Then you should add this text code to the invoices in the archive batch. Change your invoice spec so the text code prints where the description is now printing.
When it comes time to update the archive batch each month, simply change the text code under Text Maintenance and run the Update Archive Batch function, checking off the Text box in the Invoice section and selecting the batches you want to update. No exporting/importing required.
Steve