Usually you will not have errors with NZ, but a little-appreciated fact is that if there is another failing library reference AND it appears in the reference list before the one that contains NZ, that would cause NZ to fail. In that case, NZ's library isn't the problem - it is a prior broken reference in the list of references. However, that should be the least of your worries because of the other things ALSO in the library that contains NZ. I would be surprised if NZ was the first such problem you ran into.
@Sarah.M - you keep on telling us that your VBA is blocked for security reasons. The issue for that blockage isn't clear, so here is my question (and I am trying to be constructive, so bear with me).
WHY is the IT group blocking your VBA? You need to know that so you can address their concerns. Blocking VBA affects well over half of the programs in the MS Office suite and, while it doesn't make them brain-dead, DOES limit their abilities significantly.
Is this Access project your idea or a response to a boss's request? When I had a similar IT restriction problem before, I went to my boss and pointed out that the IT staff was in the way and was preventing me from making headway. I told the IT person who was responsible for the blockage that I was building something at the request of a higher-up and that from now on, HE would be called when I failed to make something happen. It is typical of IT folks to go overboard, but by blocking Office VBA, you make it impossible to do certain things that are typically desirable in an office. Sometimes, your best solution isn't to work around a blockage but to clear the blockage. Technical solutions go only so far no matter how big, but small political solutions can often make a big difference.