With Auto Lock set to 1 minute, the phone powers off when it is supposed to go into sleep mode. I then have to power it back on and the phone then boots up.

I've restored the firmware (1.1.4) and the problem remains even before jailbreak/unlock.

The problem started happening several days after installing 1.1.4 and then using iUnlock 2.0b on it, although it could have nothing to do with it.

Any suggestions.