I experienced this problem as well with Brave New World and updated to the latest patch, right here and now on September 2013 and on Windows 7 SP1.
This is basically down to severe memory leaks with the poorly optimized Civ5, which is why people tend to notice it the most after a number of hours of gameplay and/or with larger maps, despite those who reported it meeting or exceeding the game's recommended specs and having all their drivers up-to-date. It's really shameful that Firaxis haven't fixed something as wildly reported as this after all this time and all the patches.
I seem to have managed to circumvent the issue with the good old Windows /3GB parameter (Civ4 players who used lots of mods and giant maps might remember this), which essentially tells your OS to use up available RAM in a more efficient way in 32-bit systems. I have now been playing for a few days without seeing that ugly grey square where the civilopedia graphics should be.
To enable it on Windows XP:
Edit your OS boot.ini and add "/3GB" (without the comment marks, obviously) to the end of the line which includes "/fastdetect", e.g.
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /3GB
To enable it on Windows 7:
Run a command prompt window (with full admin privileges) and enter:
Code:
bcdedit /set IncreaseUserVa 3072
If you need to disable it later, enter:
Code:
bcdedit /deletevalue IncreaseUserVa
Note that you'll need to restart your system after any of these modifications to apply them.
Please post confirmation here if this fixes the problem for you, since this issue persists to this day and thus other players might benefit from this.