mkultra dont work with r:r ?

ok when i first got resistance retribution, mkultra worked fine with it. then i installed that xmb eboot loader plugin, which didnt do what i wanted it to do, so i uninstalled it. but then when i got on r:r with mkultra on, it said i failed to connect as soon as i pressed infrastructure. mk did this to me even when i didnt press home , vol up/dn or anything to activate it and when i turned off mk in recovery, i could get online again. i tried re-d/loading and installing vers. 3 and 4 but they both gave me the same problem. anybody know what the deal is with that? not a real big deal, nitepr revk still works, but i prefer mk