Whiteouts with ensuing assertion failure

Hi all. I am experiencing occasional whiteout of certain blocks (buildings mostly) after playing for awhile and being around a lot of AoE users or flying around the city. I start to feel some lag and then spy a whited out chunk of background as I turn or something. Things get progressively worse and then crash with an assertion failure.
My system: Macbook Pro, OS 10.7.3, 4GB Ram, Intel HD graphics
My Settings: Shadows-lowest, Water-low, reflections-off, physics & texture- medium, character texture-high, world detail-89%, shader-high, suppress fx-on

What is the culprit of assertion failure usually? I've heard it is graphics and have lowered settings, but it does still happen occasionally.
Thanks.

Sounds a bit like the system is overheating, since it only happens after playing for a while. Lower the shader level to medium, or using /maxfps to limit the FPS to a lower peak can help some with lower the load on the system.

We've been saving Paragon City for eight and a half years. It's time to do it one more time.

Try /reloadgfx every now and then. It may take a few tries.

Try to get a temperature monitoring program for your CPU and graphics card.
Something like HWmonitor works.

You want to keep everything as low temperature as possible. The CPU should be under 60 degrees Celsius, approximately 130 degrees Fahrenheit , and the graphics card needs to be under 80 degrees Celsius or it will likely get up to 100 really quickly, 212 degrees Fahrenheit(literally boiling).