Hi Gallery-plugin expert,
I've suffered this issue with at least 3~4 plugin updates - but it's still there.
The red upload button was there, with original WP 3.5.2, but it was short time - someday I lost that button, and unfortunately the "add media" button (provided by WP itself) also doesn't work (but it works for any other pages except gallery).
Then, according to search result, I checked directories permissions from wp-contents to uploads of gallery-plugins and make sure all of them are 755, but no luck.
Now I update my site to WP 3.6, but the issue still exists, the only way I add images into an existing gallery page is - add it through media library uploader, and manually attach them ONE BY ONE into existing posts/pages - then choose the gallery page - that really brings me too much work load.
PLEASE HELP~~~ RIGHT NOW~~~
Thanks in advance.
Fisherworks from http://fisherworks.cn