If you just ripped your copy of DJ MAX Fever and noticed it's freezing alot on your custom firmware a couple of things you need to do. First off, set your UMD mode to NO UMD SONY in your recovery menu...
Using UMDGen patch the game with the ppf file posted below and save it to CSO level 9 compression and it should work on the memory card now.
UMDGen can be found on the 'Howto: Rip your own UMD's' thread under tutorials and guides section of this site.
This patch is for the US Version of DJ MAX Fever, and fixes the flickering screen bug and should keep it from freezing up the psp.