Need help with a nested IF w/ISNA vlookup formula

If indeed it's the case that "the ONLY thing that has changed from the last file and this file is the list of active employees" then the problem isn't that the formula isn't working; it's something about or in that new list of active employees. That error means data is not available. (When one of my spreadsheets returns that error, when looking for things in a newly downloaded data file, I can always trace it back to some kind of change in the data itself.) 

I would suggest leaving the formula alone and taking a close look at the data.