I kno God didnt create evil.. but??

i consider myself a pretty strong christian but the other day someone asked me a question nd i couldnt answer it.. nd i was sooo sad i juz didnt understand.. they say if evil cannot enter the kingdom then how did the angel lucifer get there... nd why did God create him there if he KNEW this was goin 2 happen.. plz o plz can sumone answer me.. nd no athiests plz.. i think too much of u have had ur share of answers on yahoo answers.. thnx :)