This never happneded to me before, I can't open the "Browse Server" box to search the image and upload. For some reason, I upload image from PC and when I save changes, it doesn't record the image uploaded. So, basically I'm not able to upload images from "Browse Server" neither uploading from PC. This only happens in K2 Categories.
In K2 Items I can upload via "Browse Server", but can't upload from PC.
Tried to find similar problems and couldn't find why I can't open "Browse Server" in K2 Categories.
I am using Joomla 3.5 and K2 v2.7.0
UPDATE: I can now upload images from PC after editing file 'category.php', replacing '===' by '=='. Although can't open dialog search from Server.