since your on dex you need to open up rebug tool box and go to spoof psid and select the cex one but i recomend you get a console id changer and google ps3 console ids so that way if you get banned it wont be your ps3 that gets banned it will be soneone elses
P.S. if you do this you wont need to spoof psid and you should be able to sign in fine