Quick Selection Tool won't deselect

I hit Crtl Z to un do it

The Quick Selection tool is a combination of a brush and the selection tools so just clicking outside the selection won't deselect, whether you hold down Alt or not. If you want to deselect then press Ctrl+D

In his CS5 book, Martin Evening teaches what he calls a “double-Q” trick. The quick selection tool learns what to select when you paint and what not to select when you alt-paint (can be option-paint on the Mac). After using the quick selection tool for a while, the learning can be so strong that it will be next to impossible to deselect a portion of the selection . But changing to quick mask mode (Q) and back (another Q) clears the learning memory of the quick selection tool, while keeping the selection made so far. Then it will be far easier to deselect what has been selected previously.

Best regards,

Antero

If you've just selected something, and it's not what you wanted, you can use Ctrl-Z to step back one step in the History (i.e., to before the selection was made), then try again with a different Tolerance setting or by clicking on a different point.

With the Quick Selection tool current, make sure you review the settings at the top of the Photoshop main window.  They affect how the tool will work:  A smaller Tolerance value will select fewer pixels, Anti-alias makes edges smoother, Contiguous will only select one block of contiguous pixels (vs. selecting similar pixels all over the image), and Sample All Layers will allow you to select based on what you see in the composite multi-layer document vs. just what's on a particular layer.

-Noel