We need to mark the XP partition inactive and the Win7 partition inactive.
The thing to remember when doing this is that you must determine without question which partition listed is the Win7 and which is the XP. Do not proceed otherwise.
Boot into the Win7 Repair console, open a Command Line and type:
DISKPART
LIST DISK
SELECT DISK # (for hard disk)
LIST PARTITION
select partition # (for XP partition ONLY, be sure by size and position)
inactive
exit
Reopen Command Line and type:
DISKPART
LIST DISK
SELECT DISK # (for hard disk)
LIST PARTITION
select partition # (for Win7 partition ONLY, be sure by size and position)
active
exit
Now try running Startup Repair 3 times. There are more commands if it doesn't work.