OpenGL ES 2.0: Can't seem to render second VBO?

Question

I have 2 VBO's and 2 IBO's in OpenGL ES 2.0. I don't have any problems rendering the first VBO but the second one doesn't get rendered. I do not get an error either.

First VBO contains a GL_STATIC_DRAW object with 9 vertices. The second VBO contains 4 vertices to create a simple 2D plane so that I can render a user interface into it.

Here's the relevant parts of my code in C. renderBG() renders the first VBO and renderUI() renders the second VBO. Am I doing this the correct way?

void renderBG(OGL_STATE_T *state) {

    matIdentity(modelViewMatrix);   
    matTranslate(modelViewMatrix, 0, 0, -1.0);

    _currentRotation = _currentRotation + 0.5;
    _currentRotation = fmod(_currentRotation, 360); 
    matRotate(modelViewMatrix, 0, 0, 45);
    matRotate(modelViewMatrix, 0, _currentRotation, 0);

    const GLfloat *mvMat = modelViewMatrix;
    const GLfloat *pMat = projectionMatrix;

    glClearColor(0, 0.05, 0, 1.0);
    glClearDepthf(10.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glViewport(0,0,state->screen_width, state->screen_height);

    glBindBuffer(GL_ARRAY_BUFFER, state->nsVB);

    glUniformMatrix4fv(_projectionUniform, 1, 0, pMat);
    glUniformMatrix4fv(_modelViewUniform, 1, 0, mvMat);

    glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0);
    glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex),
            (GLvoid *) (sizeof(float) * 3));

    glEnableVertexAttribArray(_positionSlot);
    glEnableVertexAttribArray(_colorSlot);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, state->nsIB);
    glDrawElements(GL_TRIANGLES, sizeof(nsIndices)/sizeof(nsIndices[0]),
            GL_UNSIGNED_BYTE, 0);

}

void renderUI(OGL_STATE_T *state) {

    matIdentity(modelViewMatrix);
    matTranslate(modelViewMatrix, 0, 0, -1.0);

    const GLfloat *mvMat2 = modelViewMatrix;
    const GLfloat *pMat2 = projectionMatrix;

    glViewport(0,0,state->screen_width, state->screen_height);

    glBindBuffer(GL_ARRAY_BUFFER, state->uiVB);

    glUniformMatrix4fv(_projectionUniform, 1, 0, pMat2);
    glUniformMatrix4fv(_modelViewUniform, 1, 0, mvMat2);

    glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0);
    glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex),
            (GLvoid *) (sizeof(float) * 3));

    glEnableVertexAttribArray(_positionSlot);
    glEnableVertexAttribArray(_colorSlot);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, state->uiIB);
    glDrawElements(GL_TRIANGLES, uiIndicesArraySize / uiIndicesElementSize,
            GL_UNSIGNED_BYTE, 0);   

    GLenum err;

    if ((err = glGetError()) != GL_NO_ERROR)
        printf("There was an error");
}

void render(OGL_STATE_T *state) {

    renderBG(state);
    renderUI(state);

    eglSwapBuffers(state->display, state->surface);
    check();
}

EDIT:

Here's some additional information. This is how the Vertex and Index arrays are populated in the second VBO:

GLfloat _width = uiWidth;
GLfloat _height = uiHeight;

Vertex uiVertices[] = {
    {{-_width,_height,0}, {1,1,1,1}},       // Top left
    {{_width,_height,0}, {1,1,1,1}},        // Top right
    {{-_width,-_height,0}, {1,1,1,1}},      // Bottom left
    {{_width,-_height,0}, {1,1,1,1}}        // Bottom right
};

GLubyte uiIndices[] = {
    0,1,2,
    2,1,3
};

uiVerticesArraySize = sizeof(uiVertices);
uiVerticesElementSize = sizeof(uiVertices[0]);
uiIndicesArraySize = sizeof(uiIndices);
uiIndicesElementSize = sizeof(uiIndices[0]);

printf("%f %f\n", uiVertices[0].Position[0], uiVertices[0].Position[1]);

glGenBuffers(1, &state->uiVB);
glBindBuffer(GL_ARRAY_BUFFER, state->uiVB);
glBufferData(GL_ARRAY_BUFFER, sizeof(uiVertices), uiVertices, GL_STATIC_DRAW);

glGenBuffers(1, &state->uiIB);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, state->uiIB);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(uiIndices), uiIndices, GL_STATIC_DRAW);

Answer 1

So turns out I had my indices declared in clockwise order (Thinking that would face the normal towards the Camera) and GL_CULL_FACE enabled. Switched the indices around and all is good with the world.