Multiple layers locked could not be unlocked

I have multiple layered Adobe Photoshop documents. Multiple layers are locked by me but not all the layers are locked. I need to modify some locked layers so I have clicked the layer then click the lock button to unlock the layer but it comes into my surprise that the layer could not be unlock. I can’t make any modification anymore unless if I will regenerate the entire layer.
I know that all layers can be unlocked even the background layer, but at this time I can not unlocked it.
I need your expertise here.
Thanks!

Adobe Photoshop CS3
Could not edit the layer because the layer is locked.
