Reoccuring problem. Status bar goes across. Pictures uploads to \tmp. Post photo button stays inert. Running Joomla 3.5.0, SIMGallery 5.1.0.

This was a problem I had before. Before it was related to a mod_security rule that prevented blank content-type headers. I have gone back to my host and here was their answer:
Hello, and thank you for contacting Hostgator regarding your Joomla issue.

Thank you for the update! I was able to log in to your installation with the provided credentials, and load the gallery page however I was not able to load the upload upload form. A blank frame is served, screenshot attached. Unfortunately, I could not determine why the page served was blank.

Continued in frame: