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:

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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

It seems to me that the easiest way would be to add a helper column ( say col "a" starting in A1), enter your formula and let the n/a happen and in the cell where you need the result enter

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Then hide the helper column

2 remarks:
-you are using full columns(B$2:$O$65536). is this really necessary? Do you have the entire column filled ? This will slow down your calculations a lot

- you start the Vlookup looking for an absolute referenced value ($f$8). Dragging the formula will not change anything at all. Depending on your needs $F8 or F$8 might be what you need

EDIT after posting : no brackets needed around the column number in your Lookup table VLOOKUP($F$8,Data!$B$2:$O$65536,2,FALSE) is OK