Can't unstack photos PSE 12

Stacking greyed out usually means it's not a stack.   A stack will always have a bunch of little "stacked" swquares in the upper right corner of the first image in the stack.

Not much to unstacking:   simply right mouse click on the stack and choose unstack.  
I mention that, even though it's pretty basic, simply because you have not said you did it. 

Hi , I've moved your post from the Photoshop forum to the Photoshop Elements forum where you are more likely to get help relevant to your issue.

Dave

in the future, to find the best place to post your message, use the list here, https://community.adobe.com/

p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post (like this one has already been moved) if it helps you get responses.

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