Dear shivanand,
At this stage of the course your should be able to define which line of the code is causing the problem. Try to execute the code line by line using F8 and try to find where is the error and fix it yourself. If you are not able to fix it, then you can share with us the file you are working on it (Please compress it in ZIP format to be able to upload it to the forums) and we can tell you where is the problem exactly.
Best Regards,
Hany Ismael