The memory error comes up if the encrypted value doesn't match the normal value.
First thing, are you pausing the game in the top left? If not it'll likely crash once you've edited one of the values.
Secondly, make sure that you are leaving the XOR value alone (don't edit the XOR key, only copy it). You want to firstly type your new number into the value for the middle "encrypted value" and then select and enter the XOR key. Then you want to edit the top value after that. Only then can you unpause the game.
If that's not working I can make a more in depth guide for only steps 4, showing each step if you need it.