Not Unlocking?

[nike45]

Sometimes here and there when I press the unlock button on top then go to press the 4 circle button in bottom left(dont know what its called) the button will not respond, and therefore not unlock. I must wait till the screen fades and try again and it always works the second time. When I am using the phone regularly the button always works though. anyone else having this problem?

[ATTDroids]

[tae_254]

This use to happen to me. Try doing a factory reset