glDrawElements causes EXC_BAD_ACCESS on iOS

Hi, i try to implement a OpenGL ES2 rendering engine, and what ever I do I get "EXC_BAD_ACCESS" when calling glDrawElements in my draw function. I use a vertex buffer object for the vertex data and one for the indices.

Here is the init function:

// generate the buffers
  GL_CHECK(glGenBuffers(1, &_vbo));
  GL_CHECK(glGenBuffers(1, &_ibo));

  // vertex data
  int vertexcount = 8;
  int structsize  = sizeof(VertexData);
  LOG_TRACE("number of vertices: %d, size of vertexdata struct: %d", vertexcount, structsize);
  GLsizeiptr sizeVertexData = sizeof(VertexData)* vertexcount;
  LOG_TRACE("sizeVertexData=%d", sizeVertexData);
  // trace the first 3 variables of container
  LOG_TRACE("vertexdata, first 3 values: x=%f|y=%f|z=%f", aVertices[0].px, aVertices[0].py, aVertices[0].pz);
  GL_CHECK(glBindBuffer(GL_ARRAY_BUFFER, _vbo));
  GL_CHECK(glBufferData(GL_ARRAY_BUFFER, sizeVertexData, &aVertices[0], GL_STATIC_DRAW ));

  // vertex indices
  GLsizeiptr sizeVertexIndex = sizeof(unsigned short)*12*3;
  LOG_TRACE("sizeVertexIndex=%d", sizeVertexIndex);
  // trace the first 3 variables of container
  LOG_TRACE("faceindices, first 3 values: A=%d|B=%d|C=%d", aIndices[0], aIndices[1], aIndices[2]);
  GL_CHECK(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _ibo));
  GL_CHECK(glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeVertexIndex, &aIndices[0], GL_STATIC_DRAW ));

  // release them
  GL_CHECK(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0));
  GL_CHECK(glBindBuffer(GL_ARRAY_BUFFER, 0));


  _iLocPosition     = shaderProgram()->attributeLocation("a_position");  
  LOG_DEBUG("_iLocPosition=%d", _iLocPosition);
  _iLocColor        = shaderProgram()->attributeLocation("a_color");
  LOG_DEBUG("_iLocColor=%d", _iLocColor);
  //_iLocNormal       = shaderProgram()->attributeLocation("a_normal");

  _iLocModelMatrix  = shaderProgram()->uniformLocation("u_modelMatrix");
  LOG_DEBUG("_iLocModelMatrix=%d", _iLocModelMatrix);

And here is the draw function:

float  m[16];
  Matrix4X4C modelMat = modelMatrix();
  modelMat.Rotate(_zRot, _xRot, _yRot);
  setModelMatrix(modelMat);
  modelMat.GetOpenGL(m);
  GL_CHECK(glUniformMatrix4fv(_iLocModelMatrix, 1, GL_FALSE, m));
  //LOG_TRACE("setting model matrix into shader to uniform id: %d", _iLocModelMatrix);
  //shaderProgram()->bind();

  // bind the buffers
  //LOG_TRACE("bind VBO & IBO");
  GL_CHECK(glBindBuffer(GL_ARRAY_BUFFER, _vbo));
  GL_CHECK(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _ibo));

  //LOG_TRACE("enable Vertex array for attribute: %d", _iLocPosition);
  GL_CHECK(glEnableVertexAttribArray(_iLocPosition));    
  //LOG_TRACE("enable Vertex array for attribute: %d", _iLocColor);
  GL_CHECK(glEnableVertexAttribArray(_iLocColor));
  //GL_CHECK(glEnableVertexAttribArray(_iLocNormal));


  void* offset = BUFFER_OFFSET(0);
  GL_CHECK(glVertexAttribPointer(_iLocPosition, VERTEX_POS_SIZE,    GL_FLOAT, GL_FALSE, sizeof(VertexData), offset)); 
  offset = BUFFER_OFFSET(VERTEX_POS_SIZE*VERTEX_ELEMENT_TYPE_SIZE);
  GL_CHECK(glVertexAttribPointer(_iLocColor,    VERTEX_COLOR_SIZE,  GL_FLOAT, GL_FALSE, sizeof(VertexData), offset));
  //GL_CHECK(glVertexAttribPointer(_iLocNormal,   VERTEX_NORMAL_SIZE, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(VERTEX_POS_SIZE*VERTEX_ELEMENT_TYPE_SIZE)));  

  GL_CHECK(glDrawElements(GL_TRIANGLES, 12*3, GL_UNSIGNED_SHORT, 0));

  //GL_CHECK(glDisableVertexAttribArray(_iLocNormal));
  GL_CHECK(glDisableVertexAttribArray(_iLocPosition));  
  GL_CHECK(glDisableVertexAttribArray(_iLocColor));

  // release them
  GL_CHECK(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0));
  GL_CHECK(glBindBuffer(GL_ARRAY_BUFFER, 0));  

The same code runs fine under Windows via the ARM OpenGL ES 2.0 emulator framework (http://www.malideveloper.com/opengl-es-20-emulator.php).

Could someone help here?