Sometimes if you are running something at too high of settings for a particular game (like a heavily modded Skyrim for example) you get a crash when either your RAM usage exceeds 4GB (due to the 32bit cap) or your VRAM exceeds your cards limits (2GB).
If you get a error specifically saying "low *video* memory" it is probably your GPU simply is bumping against the max it can do, then something pushes it over and the game crashes to save the card from possible damage (or lockup). This tends to happen when you've modded the game heavily, the game is poorly optimized and "leaks" over time, or you have the settings higher than the VRAM can handle (some games like GTA V require over 4GB of VRAM for higher settings now).
I'm afraid the only...