What causes this type of error?

Assert @ C:\Projects\P4\SinsEntrench\Release\CodeSource\Engine/Render/Texture/FileCubeTexture.cpp(77)

DirectXAssert: [!FAILED(dxVerifyHR)]
Context: D3DXCreateCubeTextureFromFile( g_Core.d3d9->GetDevice(), fullFileName, &d3dCubeTexture)
HR: (E_FAIL)-An undetermined error occurred

This happened after i removed the mip maps from the skybox enviroment cube textures. However when i removed the textures themselves from the mod, the error still happens. So now i'm clueless.

EDIT: i removed all of the edited skybox textures, and the error went away, but i am still clueless as to why any kind of change in the environment cube texture file would cause this error.