It were the brackets wot dun it

=IF(ISNA(VLOOKUP($B20,Belgium07ComplaintQ4,{4,5,6,7,8,9,10,11,12,13},FALSE)),"",VLOOKUP($B20,Belgium07ComplaintQ4,{4,5,6,7,8,9,10,11,12,13},FALSE))

Your vlookup is wrong. The format is:
vlookup(lookup_value,table_array,col_index_number,range_lookup) For example
if  A1 contains b then
=VLOOKUP(A1,{"a",100;"b",200;"c",300},2,0)  returns 200. The lookup_value is
the value you're trying to find. table_array is the list you're looking in.
The table_array is specified by the array constant
{"a",100;"b",200;"c",300}where the commas are column separators and the
semicolons are row separators.
In this case there are 3 rows with 2 columns each row. Row 1 column 1 has
"a", row 1 column 2 has 100, row 2 column 1 has "b", row 2 column 2 has 200,
row 3 column 1 has "c" and row 3 column 2 has 300. The column_index_number
is 2 - i.e return the value in column 2 if the lookup_value is found in
column 1
of the table_array. The range_lookup is 0 (FALSE) meaning there has to be an
exact match. In this case A1 contains b, so the lookup function finds an
exact match of  in row 2 column 1 of the table, the b,  and returns column
2 - i.e. 200   From the way you have constructed your formula, I have no
idea what you're trying to accomplish.

Tyro