An error was found in a directory's cluster chain

[NoComprende]

I just tried running PGP's freespace wipe and got that message. It suggested running scandisk, but I had just run scandisk right before trying freespace wipe.

Can anyone help out with these questions:

1.) What does this error mean about the condition of my hd?
2.) How long can I use this hd in that condition?
3.) Is there anything other than MS scandisk that can take care of it me?

Thanks.