=IF(ISNA(IF(C43=99,VLOOKUP(B43,'Endur NA'!D:R,15,FALSE),0)),IF(C43=99,VLOOKUP(B43,'Endur NA'!D:R,15,FALSE),0))

Basically, if the formula looks up C43 and finds 99,then perform the vlookup and the specified tab. If not, return 0 however its returning "FALSE". Any ideas? Thanks in advance.