Hi baltwo and Miacc,
I also have a LaCie ext HD of 1T and OS 10.7.5. Since Dec 24th 2012 I haven't been able to mount the LaCie disk. I can see it in the Disk Utility but I cannot mounted. I verified the disk and even repaired it but nothing has happened, actually there is nothing wrong with the disk, but it cannot be mounted.
I did what you suggested baltwo but I'm in the same situation as before. I cannot mount the disk and/or do Time Machine.