Eraser tool deletes layer.

Also , if the layer is all one color and this is happening, check you are not using the magic eraser tool (it shares the same slot in the tool bar as the conventional eraser)

Dave

When you say deletes the layer, do you mean the entire layer is gone or all the pixel information on that layer is gone? If the former, try resetting your preferences; if the later, check your brush size.

Using a mask is a much better way to delete part of a layer, as if you make a mistake, you can correct it later.