Or sometimes the donor manager just crashes (or just stops working) without any error message or any feedback.When I try to import an excel file, I get error 23 (excel file format is invalid).
Here is what I suggest trying with the Donor Manager and Excel are having trouble communicating and you are getting an "Excel File Format Invalid" error message.
Open the file in Excel, and resave it under a new name, but set the file type ("Save As ..." to Excel 5.0 / Excel 95.
That will usually put you back in business.
Close Excel.
Now, try pointing the Donor Manager to that newly create file. That usually works.