Hello i have a problem. I have a formula that i need to edit, when i try to it always changes where it is looking for its data resulting in a #ref error Here is my code


=IF(ISNA(VLOOKUP(D17&" "&(E17)&" "&(F17),'Copy of autoupdater.xls'!TaskData,3,FALSE)),"",VLOOKUP(D17&" "&(E17)&" "&(F17),'Copy of autoupdater.xls'!TaskData,3,FALSE))

but when i even click a mouse on it and then select somewhere else on the sheet it changes to

=IF(ISNA(VLOOKUP(D17&" "&(E17)&" "&(F17),'TABNAME'!TaskData,3,FALSE)),"",VLOOKUP(D17&" "&(E17)&" "&(F17),'TABNAME'!TaskData,3,FALSE))

What am i doing or how can i edit the formula while leaving it like the first example. Please help

Jason