OpenGL: glDrawArrays & glDrawElements

Error 1:

当我在程序中调用 

glDrawArrays(GL_TRIANGLES, 0, 3 * o.numTriangles);

我check到 0x0505 即 out of memory 到 OpenGL error。
No ideas for now :(

PS 1:

I found sometimes glDrawElements is more effecient than glDrawArrays.

PS2:

I'll keep finding some thing about them. Forgive my english expression ;) Any comments will be appreciated