Why does my BlackBerry Curve keep saying to insert a sim card but there is a sim card in it?

Any suggestions how to resolve this problem please my sim is a new one

Is it backwards or is it in far enough?

Posted via CB10

Has it worked with the current SIM before, but now it gives the error?
OR
Is it a new SIM never used in the Curve?

If either, it may be the SIM is bad. Check with your carrier.

If second, your Curve may not be unlocked to the carrier whose SIM you wish to use. Confirm that your Curve is unlocked and that the carrier you wish to use does support your device.