A family of Microsoft relational database management systems designed for ease of use.
"I opened the tables in datasheet view, without running the query. What am I looking for?"
We are confirming that the AS400 table itself is properly linked.
Now that i see that line, it occurs to me the problem is NOT in the AS400 table. It looks like you may have a problem with Excel, and frankly, that makes more sense given the nature of the error (installable ISAM).
For a long time now I've preferred the fully qualified syntax for DoCmd functions because they can help identify problems. When I do that with YOUR line of code, I see that acSpreadsheetTypeExcel10 is not one of the options offered for SpreadsheetType.
Here's how that might look with one of the valid constants:
DoCmd.TransferSpreadsheet transfertype:=acExport, spreadsheetType:=acSpreadsheetTypeExcel12Xml, TableName:="DETAIL OVERDUE", FileName:=vrootdir & efile, HasFieldNames:=False
Going to the documentation for TransferSpreadsheet, I see the same thing, no "acSpreadsheetTypeExcel10 ", although the value might correspond to 2003, if it were a valid one. So I'm going to suggest you look there next, rather than at the AS400 tables.