This insert sim fault is very common which comes in nokia handsets of dct4 models mostly, it can be of many reasons, like sim ic damaged or supply not comes from power ic , uem or even of battery connector middle pin if not connecting with the battery properly.
But now the solution is in some other way and its a good shortcut that is invented. One very good shortcut is just remove the small capacitor which is placed on the left upper corner of the UEM power ic that is shown right in the picture here and after that you have also to short one pin of the sim tray i.e. on pin on the left lower side. By doing this, insert sim fault will get ok, its 100% tested solution. For more info, contact at yahoo id on this site given.