Hi NaomiB1, thanks for joining this thread. 

The maximum number of rows when importing a spreadsheet is 1000 (with a max file size of 350 KB). If you continue to see the error when attempting the import on more than one web browser, please try shortening the date range and upload transactions in smaller chunks. 

This will help to identify if there are any transactions causing an issue with the import (for example containing an unsupported special character). Get back to us below if this doesn't fix!