First try removing the sim card and carefully reinserting it. If that doesn't work and you have a friend with a compatible sim card, try inserting it. If neither sim card is working, there may be a problem with the electrical contacts in your sim card slot. Try cleaning the contacts in the slot and on the card. If this doesn't work, you can try purchasing a replacement SIM card from your wireless provider or having your phone repaired.
May be your sim is slightly dislodged ..Try to remove and place it again... If you still get that error it might be the network restriction in your phone that does not support your sim network..did you try to insert some other network sim card? In this case you can get it your phone network unlocked from any vendors online like http://www.prounlocking.com