Not sure what you're after here - do you want the formula to include the line you've inserted, skip it or ignore it?
If you don't want the formula to include the inserted line, then you should either insert it below the limit of the fornula or (more complicated) edit the formula to skip the inserted line - something like sum(b3:b6)+sum(b8:b10) thereby skipping row 7. There may be a more elegant way of getting around your problem, but unless you HAVE to insert a line in the middle of a series that are being summed why do so?

Jon