I think your table is corrupted.
If you can open the table try this:
Use YourTable
copy to NewTable cdx
use
delete file YourTable.dbf
delete file YourTable.fpt
delete file YourTable.cdx
rename NewTable.dbf yourtable.dbf
rename NewTable.cdx yourtable.cdx
rename NewTable.FPT yourtable.FPT
>I've added a new field to an existing table, and am trying to reindex it. Now, I get the error message that the table is invalid and needs to be validated? Also, when I try to open it in the editor, the message that the .dbf file did not match the entries in the database. I've added fields to my tables before and have never had this problem. What did I do differently?