Problem regarding #NAME and #N/A error messages when pulling data across sheets

Our company uses a large excel document to keep track of over 400 of our members, everything has been working fine, but all of a sudden on one of the tabs, we've received several rows of #NAME and #N/A error messages. The formulas still look fine to us and we really just don't understand what the issue is. Here are some samples of formulas that are giving us issues:
(#N/A):

=SUM('Statistics (Total)'!B83:B84)

(#NAME):

=(E31/$E$9)
='Statistics (Total)'!B74

Thanks, we'd be more than willing to forward on any additional info to help solve these issues