Error in moving to next lesson

My friend have completed till 13th lesson. He is at the last stage of 13th lesson. The 14th lesson is not getting unlocked. Can anybody help me in this issue.

please check out if all previous chapters are completed or not(). if it get completed when you on hover the the videos(x/163) left bar will be in green color, if any of previous is in yellow that means that person have not finished that chapter completely. or if any of the test he reopens even after he finished once she should attempt to clear that level. make sure left bar for all chapter are in green color.