I Have the following formula giving me #VALUE! error when i want to have it result in n/a if there isn't any data.
=IFERROR(HLOOKUP($N80,RP!$C$12:$BR$55,$D80,FALSE),"n/a")+IFERROR(HLOOKUP($N80,FG!$C$12:$BR$55,$D80,FALSE),"n/a")
Use one IFERROR function for the whole expression.
=IFERROR(
HLOOKUP($N80,RP!$C$12:$BR$55,$D80,FALSE) +
HLOOKUP($N80,FG!$C$12:$BR$55,$D80,FALSE),
"n/a")