Addition of ISNA or ISERROR to current IF & VLOOKUP Formula

Hi all, Just wondered if anyone could help me with this formula, I've tried a few different combinations but can't get them to work. I'm fairly new to the more complex excel formulas so any help would be much appreciated.

Basically I have this formula which works fine:

=IF($E$28=0,VLOOKUP($F$8,Data!$B$2:$O$65536,{2},FALSE),VLOOKUP($E$28,Data!$A$2:$O$65536,{1},FALSE))

Except when I'm not asking it to look anything up it has #N/A sat in the cell. I know i need to as and iserror or an isnumber function somewhere but I can't seem to get it right! I just want the cell blank when not in use...

Cheers,
Dan