Hi all,
I need to create a data validation drop down that checks for uniqueness over
the list it's part of and dependant on content of another list... here's what
I mean:

ColA ColB
ABC 123
ABC 234
ABC <validation checks that the entry belongs to ABC and is not 123 or 234
DFE <validation allows entry of 123 because DFE doesn't have it

Now, I can produce a drop down list dependant on another column thanks to
http://www.contextures.com/xlDataVal13.html :

OFFSET(ColAStart,MATCH(B3,AllColA,0)-1,1,COUNTIF(AllColA,B3),1)

I can also check for uniqueness formula with this formula:

ISNA(VLOOKUP(B3,B$2:B2,1,FALSE))

Both formulas are working well in other places. My thought is that I can
combine them with the Offset formula as the VLookup formula's lookup range,
so:

ISNA(VLOOKUP(B3,<that offset function,1,FALSE))

However, nothing happens... no error, no list...?

If I copy that formula out to another blank sheet to break it down and test
it I get a circular reference error.

I can't have the ColB entries elsewhere as this is where the ColB list is to
be created. Can anyone help?

TIA, Sara