Lateral Entry to IGNOU has  been stopped in 2005. Even the official website doesn't speak about any Lateral Entry for MCA. According to the official website http://www.ignou.ac.in/ignou/aboutignou/school/socis/programmes/detail/174/2 you should have completed your Bachelor's degree in any stream to be eligible for MCA. And you should have have studied Mathematics as one of your subjects either at your 10+22 or Graduation level. If you haven't studied Mathematics at any of these levels, then you have to take up BCS-012 course.