MDAC 2.5 SDK - ODBC Desktop Database Drivers
When the Microsoft Access, dBASE, or Paradox driver is used, the syntax of the DROP INDEX statement is "DROP INDEX a on b" where "a" is the name of the index and "b" is the name of the table (not DROP INDEX index-name).
When the Paradox driver is used, the DROP INDEX statement deletes Paradox secondary index files.
The DROP INDEX statement is not supported for the Microsoft Excel or Text drivers.