When clicking "Map Fields" for a DAT file import, an error appears and the field mapping dialog does not appear. The error message is:
"File contains header but no valid record"
1) Verify that the proper delimiters have been selected.
2) If the delimiters are correct, then the error could be caused by a mismatch between the number of fields in the field definition line, and the number of field values in the record definition lines.
E.g. if there are 25 field names in field definition line 1, but 26 field values in the subsequent lines (lines 2 and beyond), then the "file contains header but no valid record" error will appear.
Tip: For this scenario, count the number of field separators on the header line, and compare with the number of field separators on other lines.