# why is glVertexAttribDivisor crashing?

I am trying to render some trees with instancing. This is rather weird, but before sleeping yesterday night, I checked the code, and it was in a running state, when I got up this morning, it is crashing when I am calling glVertexAttribDivisor I haven't changed any code since yesterday.

Here is how I am sending data to GPU for instancing.

    glGenBuffers(1, &iVBO);
glBindBuffer(GL_ARRAY_BUFFER, iVBO);
glBufferData(GL_ARRAY_BUFFER, (ml_instance->i_positions.size()*sizeof(glm::vec4)) , NULL, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, 0, (ml_instance->i_positions.size()*sizeof(glm::vec4)), &ml_instance->i_positions[0]);


And then in vertex specification--

    glBindBuffer(GL_ARRAY_BUFFER, iVBO);
glVertexAttribPointer(i_positions, 4, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(i_positions);
glVertexAttribDivisor(i_positions,1); // **THIS IS WHERE THE PROGRAM CRASHES**

glDrawElementsInstanced(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, 0,TREES_INSTANCE_COUNT);


I have checked ml_instance->i_positions, it has all the data that needs to render.

I have checked the value of i_positions in vertex shader, it is the same as whatever I have defined there.

I am little out of ideas here, everything looks pretty much fine. What am I missing?

I ran the program in debug mode, and found out that glVertexAttribPointer was NULL. After restarting my windows the program started running like it was before.