I get the following Error Message about 40% to 50% of the time since I've started using v8.4. I first updated from v.7 to each succesive version after that one and ended up cleaning out the old installation and directory completely and started over with v8.4 as a clean install with a database to boot.
It has become so frustrating to the point that I at times want to just say the heck with it and find some other blog software package but I figured I'd check here first and see if anyone has an any idea as to why this issue keeps coming up, mainly in the Admin panel but also from the blog itself. I use Ctrl F5 a lot but not to too much success:

Edit: Actually this problem started when I went from the last version of 7.1 to version 8.0, 8.1, 8.2. 8.3 and now 8.4 and has never gone away since.