Hi.
What appears to have happened is you installed Linux Mint "Daryna" to the MBR when you first installed it, but then when you installed Linux Mint "Elyssa" you erased your old installation but not the master boot record (MBR). So, GRUB is still trying to load the old operating system (in this case, Linux Mint "Daryna") when it should be loading the new operating system. This appears to be the problem, anyhow.
So, boot up from the live CD (you were correct! Ha!). Open up a terminal, type 'sudo grub-install /dev/sda'. I think that's correct, anyhow. It should work. This will rewrite your master boot record, loading the new operating system and Windows XP.
If you're really interested, here's some stuff to read up on:
4. Grub Error 15
Situation
This error can occur in two different stages of the GRUB configuration, either during the initial configuration (installing GRUB in the master boot record) or after booting the system and attempting to launch Linux (or any other entry).
Code Listing 4.1: Grub Output - Initial Configuration
grub> root (hd0,0)
Filesystem type is xfs, partition type 0x83
grub> setup (hd0)
Checking if "/boot/grub/stage1" exists... no
Checking if "/grub/stage1" exists... no
Error 15: File not found
Code Listing 4.2: Grub Output - Booting an Entry
Booting 'gentoo Linux'
root (hd0,0)
Filesystem type is ext2fs, partition type 0x83
kernel (hd0,0)/boot/kernel-2.4.20 root=/dev/hda3 vga=792
Error 15: File not found
Press any key to continue...
Astronomiconal