In the middle of working on this file, all the layers in the file suddenly had erasure patterns all over the images. I tried undoing my last few steps, and it just undid the actual work I did. I thought it might be a workspace problem or something, but I saved my file when I saw it start happening and sure enough all my layers are unusable now. :( I just want to know why this happened so I can prevent it from happening next time. I wasn't doing anything too crazy, just image layers and using the selection/brush/dodge tool. Thanks for any help.