Mmm.. that copy of hdparm is _ancient_, and I do know there was a bugfix related to the secure erase stuff, in hdparm-9.26.

The current version is 9.27, at sourceforge.

Now, I just tried 9.16 here, and it erases the SSDs I have on hand. But the Intel SSD you have supports the "enhanced erase" mode, which cares about that bugfix.

So.. I suppose the thing to do, is either (1) use Intel's own SSD toolkit with their funky drive, or (2) give hdparm-9.27 a try first.

Cheers

-ml