Eraser tool not working on layer
Hello!
I am very new to Photoshop having only started using it a week ago. I was trying out some photo painting effect and it worked out great the first time. However, just yesterday, in the middle of swapping pictures to edit, my eraser tool got a bit 'wonky'. I cannot seem to erase on a layer but it appears to be working on the thumbnail.

What i did was use the magic wand for selection, inverted the selection, copied as layer, filled the background, then tried to erase on the layer.
Any help given would be greatly appreciated!!! I'm using PS CS4 on windows 7, intel quad core with 4GB RAM, no tablet installed.
