corrupt file or cs5 problem

This is a first for me. I have no idea what is causing this problem.

first shot, I open a file, created a layer mask. When adjusting the mask, white lines appears.

I then opened an already edited PSD file. I converted it to 8bit, and the green lines appeared.

what the hell.

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Well, it doesn't ring a bell for me -- maybe contact Photoshop support and send them these images, or jump into the Photoshop Users Forum?

What are we looking at?

You are saying the image is fine until you adjust the layer mask?

Screenshot of the layers palette maybe?

I assume, correct me if I'm wrong, that we are looking at two completely different images here, and that you have worked on both images before this current problem.
Can you pull up the images before applying any alterations with them looking normal and the difficulty starts during the workflow? Is it a repeatable problem starting from the RAW image?

I assume that you have tried rebooting your system. Failing that, a un/reinstall of CS5 may be a PITA alternative.