Did you try it? That won't work at all, since ISERR will always return
FALSE when passed #N/A!
From XL Help:
ISERR
Returns the logical value TRUE if value refers to any error value
except #N/A; otherwise it returns FALSE.
One could use ISERROR(), which does trap #N/A, but that would mask other
errors as well. Better to use ISNA
=IF(ISNA(VLOOKUP(...)),"",VLOOKUP(...))
though out of sheer cussedness I prefer the slightly more efficient
=IF(ISNA(MATCH(A1,J:J,FALSE)),"",VLOOKUP(A1,J:K,2,FALSE))