Kind of confused what you're wanting. If you just want to replace a null value then just do this
IIF(IsNull(DLookUp("VenueName","EmployeeDeptVenueNameT","VenueID=" & [TLVenueID])),"N/A",Enter What To Do If False Here)

If you want to replace N/A then
IIF(DLOOKUP("VenueName","EmployeeDeptVenueNameT","VenueID=" & [TLVenueID])="N/A",True Part, False Part)

Thanks for gettting back to me.

No I'm not trying to replace a Null value. I usually use the Nz Function for that, but I'm finding the IFF isnull seems to be a better route with my database.

For example with our departments we have F&B Grill, F&B Deli, F&B Admin. Other departments like security do not have multiple venues so those associated IDs, the venue name is just "N/A". So I'm only wanting to replace/omit "N/A". That way the entries for Security Officer, the department will come up as "Security" rather than "Security N/A".

I know it sounds kind of confusing how I have it set up, but I have venues in all of the departments with "N/A" so the cascading dropdown boxes work. We also have "STEP" employees (strengthen tribal employment program) for each department, so each department at least has "N/A" and "STEP" as venues. I'm just trying to replace/omit any entries that would have "N/A" so it doesn't list "Gift Shop N/A".

Hopefully that makes sense.

I don't think the replace function would work with that code because the "N/A" exists in the "VenueName" field, not the TLVenueID. TLVenueIDs are strictly numbers.

I included a screenshot of the report, so you can get a visual of what I'm referring to. I personally wouldn't organize this information in this format, but I'm trying to mirror an already existing report from a different system.

Oh OK so you just want to take that N/A off if it's set to the field.

So you can just do this for the control source

=DLookUp("DeptName","EmployeeDepartmentNameT","DeptID=" & [TLDeptID]) & IIF(DLookUp("VenueName","EmployeeDeptVenueNameT","VenueID=" & [TLVenueID])="N/A",""," " & DLookUp("VenueName","EmployeeDeptVenueNameT","VenueID=" & [TLVenueID])

Hey Adam! Had to throw in one more parenthesis to close the IFF statement, otherwise, it works like a charm. Thank you very much! As said above, this is extremely helpful because I can get away from one of the queries I previously used for a replace function. I figured it could be accomplished with an IIF statement, I just didn't know how. So thank you very much!!!!

Woops, yea I missed that good catch :P. No problem