The error message is generated as SelectPay is unable to read the file with the information that has been selected. Listed below are potential solutions.
File format
Check the import follows the template correctly.
Ensure the file is saved as either, CSV (comma delimited) or Text (tab delimited).
Ensure the correct import format is select based on the file type.
If you are still having issues after checking the above, raise a case, attaching a copy of the import file.