I am not taking any credit for this method, but I tried it on dark void and it worked for getting me grease monkey
What the method does is, it forces the game into rewriting any info stored on your profile for a particular game, so it basically puts the game back to the first time u played it (i.e no levels, no upgrades, no journals)
The way i applied the method was:
1) Put your profile on a usb or memory stick. I personally had deleted dark voids saves in attempt to unglitch grease monkey orignally, so i had no saves to worry about.
2)Clear System cache ( google it if you unsure)
3) Start Dark void, decline the update, and on the CAPCOM screen pull out ur usb.
4) U will now have a msg to insert usb, ignore it. Go to the main menu and check if u have any journals etc. If you have nothing it has worked.
5) Insert you memory card, and start a new game ( this should be your only option if it has worked) once your in the game, just save it and back out.
*Edit: IF THIS CAUSES YOUR GAME TO CRASH AT THE CHAPTER 1 SCREEN, JUST GO INTO OPTIONS ON THE MAIN MENU AND CHANGE DIFFICULTY, SO THE GAME AUTOSAVES (credit Jeffty X360A)
6) You are not save to accept the update and play the game online.
I then had to replay the most of the game, but fortunately, on 2-4 ( the level you grind) you get the last weapon, so you dont need to go any further!
Hope this helps, and again I dont take any credit for the method! I am so happy to finally have 1k in this game!
*Edit: For the record, I played as far as 2-4 and then continued to grind points by replaying chapter till I had in excess of 142k. I then began to upgrade using the box in the level, by the method of buying 1 upgrade, firing a few rounds, buying next upgrade, firing a few rounds etc etc. My achievement unlocked as I exited the box after buying the last jet pack upgrade.