I've been fighting with my website for months. I have had lots of little problems and couldn't find anyway to solve them. I was pondering today on how I could backup my entire website and rebuild it from scratch. It wasn't looking promising, as there are thousands of files on there now that would probably have to be moved over individually and many other pages that would have to be recreated.
So, I was poking around the directory structure on the web server, just trying to figure out how I was going to do this... I started realizing that there were a lot of files there that seemed to be duplicates of other files. Checking into the file dates, and comparing them to the recently downloaded copies of DNN, I realized that a lot of them were left over from previous versions of DNN (I had upgraded that website many-many times).
That got me thinking, I had recalled that I had fixed a problem several months back by deleting an older file that was causing a conflict. So, on a whim, I went through the entire DNN directory structure and moved all files that had date/time stamps that were older (and didn't appear to be from a third-party module) to temporary subdirectories (so I could easily move them back if I had to).
When I got done, I tested out the website, and almost all my glitches were gone! It was running smooth, and seemed to respond faster. I have a fully-functional (almost) website again! WooHoo!
So, if you've upgraded your website many times, installing over the top of the previous one, that might be something to check into. Apparently DNN will use the older files if it finds them, regardless of the version #.