Undefined function 'Nz' in expression

The Nz function is most likely in a view/query you are referencing in one of your many joins. You'll have to look through all of them.

As Nz() is a function of the Access application and not the Access driver, it will fail anytime you try to use it from outside the Access application. You can replace the Nz with an IIf(IsNull()) construct.

See documentation for IIf and IsNull

When put together:

Nz(expr, [valueifnull])

becomes

IIf(IsNull(expr), valueifnull, valueifnotnull)

Examples

Default: Nz(tbl.A) => IIf(IsNull(tbl.A), '', tbl.A)

With fallback: Nz(tbl.A, tbl.B) => IIf(IsNull(tbl.A), tbl.B, tbl.A)