Error message while using DiskWarrior

iMac with 8 gb ram
Os X: 10.7.1
DiskWarrior 4.3

I've had a problem with DiskWarrior. While rebuilding the Lion Directory, a task which I do every six weeks or so, DiskWarrior stopped working and I got the message shown in the thumbnail.

I've written to the manufacturers but they haven't responded as yet and I was wondering can anyone here throw any light on it.

As I understand it I'm using the proper version for Lion so I can't understand the nature of the error message

I bought DW in the shops three and a half years ago, updated it as new versions became available, and never had any trouble until now. I usually run it from an external drive as starting from the DW cd on my iMac is not an option. The Licence seems ok, I've clicked on about and there it is, but I'm a bit confused as to nature of 4.3. Is it a free update for existing licence holders or was it a free trial that has now expired? It's not really clear from the Alsoft website.

Hope some DW users can help with this.

Is there another solution to the fragmented Directory in Mac OS X? Something else I can use other than Disk Warrior?