Not sure why that'd happen tbh. Its a simple programming error, but it sounds like it'd be a cookie issue for you. That message is generally given when the included file is not found (duh). An included file is used for various situations, for example, I would guess that the entire website uses various included files. It simplifies programming by a lot. If there's a piece of code a lot of your webpages use, you can make it easier on yourself by simply putting it in another file and include it on the pages that use it, instead of rewriting it every time. It also makes it easier on you, as instead of rewriting it on EVERY page that uses it if you need to change it, you simply need to change the content of the file.
From that error message, I would guess the vba_global_error.php file either doesn't exist, or is routed the wrong way. The include_path tells you that is supposed to start the routing from usr/local/lib/php, and then extend it with /includes/vba_global_error.php. Not sure why you'd get an error message for that, but its possible qcdn uses a different php version then the board is written in, which would possibly have changed the command used, but I'd be surprised if that was the issue. Another possibility is that its a simple permission error, but it shouldn't give that error then. Kind of rusty on php, so its not as easy for me to tell you what error messages mean anymore in php. Especially if I its not code I haven't written myself.
Either way, guessing you don't get the problem now simply because you don't get an error message, which is the file it attempted to load earlier. Did you try clearing your cookies in firefox?
Not sure if that was possible earlier, but I somehow doubt I gained mod powers in the profile section while I was at work, so I will assume its been there since the update.
^