not knowing exactly what the script has I can only guess. However...
Leads to be think it trying to load the primary slave (hdb). Not the secondary master or slave.mounting //dev/hdb4 on //mnt and //dev/hdb7 on //mnt7
The error you got means it could not find a FAT32 filesystem on hdb7. Since parition 7 of a tivo disk contains a backup of the root partition (4) I guess is it is trying to load both of them to update something (presumably drivers of some sort).
If that is the case, it sure as hell isn't a FAT partition. What is in that script file on the floppy?