I’m having the same issue FYI. Just cropped up over the past few weeks (I’ve only been working on our website since Aug 1st). I’ve uploaded 12 Galleries to be used with Portfolios at the beginning of August, and all work fine. Haven’t uploaded a gallery in the past week or so, but tried to do today and finding the same problem as mentioned here.
Plugins installed are:
Askimet
Contact Form 7
Envato WordPress Toolkit
Google Analytics for WordPress
Gravitate Event Tracking
MailChimp
oAuth Twitter Feed for Developers
Redirection
Revolution Slider
W3 Total Cache
WordPress SEO
Most of those were installed before I started uploading galleries initially.
Only other major change is upgrading Dante to recent version (today, before noticing the issue with the gallery). I tried to upgrade a few weeks ago (there was a bug causing website to not load, so I rolled it back). But we only recently installed Dante, so we’ve never been on a particularly old version.