Getting around #N/A

My sheet calculates survey answers, sums the answers per category/subject and calculates the percentage of the total score for that category. The formula works in such a way as to keep calculating even if you delete a row, this is key.

The concern I have is the #N/A in the next cell down after I delete a row. If the calculation is still working - fine! If it isn't I need to do one of two things:

1. Add an exclusion to the #N/A if possible to continue the formula calculation or
2. add a tick box for keep/delete the question/row and then calculate IF the question is valid.

Sadly my ability with Excel stops here