Uncaught TypeError: Cannot ready property 'ChildNodes' of Null

When I try to add "<br /><br />" after the first table closure I get the error Uncaught TypeError: Cannot ready property 'ChildNodes' of Null however if I add it before the second table, it works perfectly fine.

I do not understand why and would like to know more as I fear there is a possible problem with my script somewhere causing this problem.