I did a quick search on that error code which returned a few things... depending on the game, the EBOOT may check the bytes (if only one is added it will not boot giving error code 80010007 on some games) or you may need to package_finalize the PKG file.
If neither of those ideas works it may be worth searching for the error code and sifting through all the results unless someone else is familiar with this issue and replies first.
i'm not making a pkg.. i'm testing whether kmeaw 3.55 CFW can run unsigned eboot.. it seems it can't..?
so I test by unself a eboot.bin from a game and then makeself back into eboot.bin - but now it won't work..!!! - it must be signed to work on cfw 3.55 i think.. so I need an app to make .elf into .bin and sign with keys.