Dave Abbott asked me to pass on this tip. I was having serious problems with PS CC when stacking images from layers. Although PS would auto align without an issue, PS would always hang after reporting 20% progress on the blend stage (Edit=>Auto Blend Layers=>Stack Images).
On the web I came across the suggestion to clear the PS settings and it seemed to solve the problem.
Start PS CC and hold down Shift+Ctrl+Alt (on Windows) until a dialog pops up asking if you want to delete Adobe Photoshop Settings file. Say yes. PS will clear the settings.
This worked for me and I hope it is useful to others.