Through Data Validation, cells in the Range A2:A26 have drop-down
lists, referring to a list in the named range Products. There are 52
items in that list.

Similarly, cells in the Range B2:B26 have drop-down lists, referring to
a list in the named range Class, with 14 items in that list.

Some (but not all) of the products in the Product list will always be
tied to specific classes in the Class list. For example, the "High
Yield" product will always have a "Fixed Income" class; the "Cash
Reserves" product will always have a "Liquidities" class.

Normally, I would use a simple Vlookup formula in column B. In this
case, however, I need to preserve the Data Validation drop-down list
capability in column B, so I can't enter formulas in those cells. A
worksheet event would be the obvious solution. I just can't seem to
come up with the appropriate code. Any help would be greatly
appreciated.