My eraser tool is not working properly :(

Question

Please excuse my bad English but it its not my firts language.
When editing pictures with photoshop, I normally create a curves layer to adjust color and then use the eraser tool over it to erase some parts of it where I don't want the curves effect to be seen (I don't know if that makes any sense). I mean, instead of using selections to edit different parts of the picture separatedly, I use the eraser tool because I have found it works better for me if I erase the effect of the parts of the picture where I don't want it to be.
The thing is, this morning I was editing and it worked fine, and suddenly the eraser stopped working on the curves layer. IF I create a new layer and draw a black line with my brush and try to erase it, it works. But it won't erase parts of the curves layer.
I have looked in the Internet for solutions and none of them have worked. I made sure the layer was not locked, I checked the opacity, I reset the tool and photoshop  itself, I then reset the whole computer, and I don't know what else to do. I use photoshop CS4 in a PC.
If someone could help me it would be very, very appreciated (:
Thank you so much!!

Answer 1

Hello, I think you should reset the colors to default using the "D" key.
In fact, you are still editing the mask, but you are applying the colors in reverse than if you were using the brush tool.
Another useful shortcut: X that will switch the foreground and background colors.