I can't verify which versions of GPsp kai use the same system as the version I have, so I'll provide a link to the exact version I'm using.
http://www.mediafire.com/?0bukzoi3nn0
If that link is broken, then check the version information in the screenshot above and search for a download on Google. You should be able to find another download. If not, PM me.
I will assume that you know how to install the emulator on your PSP. After all, you're just replacing the version you already have, unless you don't need to update it. If you do need help on this subject, look on YouTube.
Now that you have everything, find and open the config file. (See image below)

open it in notepad, wordpad, or whatever program you like, but you'll want a search function. Most programs do. Search for the name of the ROM you used to patch the Hack on to. Mine is Fire Red. You will see somehing like this:

This is where the game name comes in! An un-modded Fire Red rom (amongs all of the others) works because its save type is in the configuration. A hack with a special Name is not configured. So here is how you add it.
You want to copy all of the original ROM's info, but replace the game_name with that of the hack. Mine would look like this:
# Pokemon: Rijon Adventures
game_name = RIJON ADVENT
game_code = BPRE
vender_code = 01
idle_loop_eliminate_target = 080008c6
flash_rom_type = 128KB
The 1st line has a # at the front. When you put a # that line is for out human eyes only. The emulator ignores it. This is how you add notes and stuff. You'll noteice that every ROM has it's name after one so it can be found by us easily. :)
The second line is where you would place the name you copied down earlier.
I don't know the relevance of the 3rd, 4th, and 5th lines, but they must be there. Just copy them. They will be the same as the base ROM.
The 6th line is the save type. This is what causes the error. Now that we have set it to 128KB in the config file, everything should work! Don't forget to save the file! :)