I have an array formula that is supposed to return a list of the unique
items from another range (I6D in this case). The Array Formula is as
follows:

=IF(ISERR(INDEX(I6D,SMALL(IF(MATCH(I6D,I6D,0)=ROW( INDIRECT("1:"&ROWS(I6D))),MATCH(I6D,I6D,0),""),ROW (INDIRECT("1:"&ROWS(I6D)))))),"",INDEX(I6D,SMALL(I F(MATCH(I6D,I6D,0)=ROW(INDIRECT("1:"&ROWS(I6D))),M ATCH(I6D,I6D,0),"
"),ROW(INDIRECT("1:"&ROWS(I6D))))))

The range I6D is a named range that comprises two other named ranges,
both of which also return unique items from two other ranges.

The problem I have is that when I6D contains the array formulas that
return those inital unique items, the above array formula returns #N/A,
however, if I COPY & PASTE VALUES for I6D, the above formula then works
correctly.

Has anybody come across this problem before and got some ideas on where
I might start to fix it?

Many thanks.