Im on the Slim with True Blue cfwv2, 2.7 update dongle.
I had the same problem, BLUS30838 release by webchella. Used Paradox's Eboot Patch. First replaced all the files including the sfo, got black screen. Second replaced all the file EXCEPT the sfo(copy back original), Multiman modified the sfo but still gotten blackscreen.
If anyone got a solution please feel free to share it.