i'm having the same problem. the permissions on the library are set already for me to read and write. any other suggestions? it's really absurd that it doesn't work. perhaps it's because i used the beta version? that one worked fine. but, not now.
edit - i actually went into the package, and the source original image files also have their permissions set to read & write. actually, every top level folder within the package is set that way, and on none of them is the option to apple permissions to folder contents available (grayed out). so... does not seem like a permissions problem at all.
also, noticed - on one image, i am using "black and white" - even the very small adjustment slider in the right side panel does not show as black and white, it's just the original image! all the adjustment sliders with an image preview within them are the same, not matter what attribute they should be adjusting. so, something is likely fundamentally wrong with the app. extremely disappointed. i am trying to do some quick adjustments for a client request.