Has your "Add Media" button stopped working?

Mine did, and I was pulling my hair out trying to figure out why.
It was still there, but It just wasn’t an active, clickable button for some reason.

It turns out it was the Simpleviewer plugin that was the problem.
I had Simpleviewer v1.x installed a while ago and created a gallery.
I have since updated to SV v2.x, and installed an older version side by side (as per their instructions explained here.

Turns out it was that extra v1 plugin causing the problem.

Just thought that it might help anyone else searching for a solution to their problem ??