Tell us what you are trying to do?
On the page: hidden link I try to use custom image size 400 x 400 px. When I first build the page it worked, but was not stable. When I had to edit the page I had to reset the cutom image size again and again. Now, while editing the page it does not work anymore. I get an error-message that says: 'Missing information for resizing image' (see screenprint).
I read the help-posts, see below and added code to my 'function.php': image sizes 'first' and 'second' (see screenprint). With regenerate thumbnails I made the two sizes. Still I cannot choose the custom sizes.
What am I doing wrong?
The fix for this has already been prepared and will be included in the next plugin update, expected shortly after Easter, although a beta is due this week.