Fatal_Error

[t-storm]

I played Civ IV yesterday and it ran fine. Today I played and right when it was done loading my the whole game ended and an error titled FATAL_ERROR came up saying this.

Your system has run out of video memory. Please trying reducing you video settings.
File:\main\civilization4.bak\SDKs\Gamebryo2_0\CoreLibs\NiDX9RenderedTextureData.cpp, Line:167

I don't know what to do. Can someone help?