Error on restore: "specify the location of the volume 2" ?

Hello! We're using Acronis True Image Home 2010. We do incremental backups to an external USBhard drive each night. Every so often, the software raid on the machine decides to go out of sync, irreparably, and we rebuild the raid and restore from backup. We've done this successfully several times before. This happened today.

Before rebuilding the RAID, I ran a validation task on the incremental backup set. It succeeded. I then destroyed and rebuilt the RAID.

After booting to the rescue disk, I pointed Acronis to the backup set on the USB hard drive. When I specified the latest member of the set, I got the error message, "Specify location of the volume 2". What is the volume 2? What is it looking for, and why have we never needed it before? After hitting 'Retry' a few times, pointing it to the Full backup ( to no success), I clicked 'cancel' and the recover started. About 80% of the way through the recover, it asked for volume 2 again. I hit cancel. The restore finished, and upon reboot, I got an MBR error.

What the heck is going on? I rebooted the restore disk and tried to point it to earlier members of the incremental set. It still asked for volume 2. Finally I pointed it to the original Full Backup member, and got no errors. We are restoring as I type.

Unfortunately I can't tell you more about which release or build number of Acronis we're using, because our system is down, and I can't find it on the bootable disk :( I can tell that I burned the rescue disk in September of last year.