One thing to try when you have got a problem that you can't solve is to try a totally different method of doing it. I would never ever use Vlookup in VBa it is a worksheet function that is geared to ranges on a worksheet and it is inflexible and slow when you try to use it in VBA. e.g you can't pick up columns to the left of the matched column
A much better way of doing the same thing is to load the range which you want to do the lookup on into a variant array (ie into memory) and then do the search by looping through with a vba loop.
In your case because you are doing 5 separate lookups just to get different column numbers it is horrendously inefficient. In this case it is not a problem because you only do it once, but if this was in a loop of 10000 then you really would notice the difference in speed between using a variant array and using vlookup
So I have recoded (but not tested) the 5 lines where you are getting the error. I can assure with my code you will not get the same error ( you wil probably get a different error but hopefully you might solve that one)
At least i will have shown you an alternative and faster way of writing the code:
With FRMLookup
'.PassRem = Application.WorksheetFunction.VLookup(CLng(FRMLookup.passNum), Sheet2.Range("Lookup"), 7, 0)
'.FirstName = Application.WorksheetFunction.VLookup(CLng(FRMLookup.passNum), Sheet2.Range("Lookup"), 3, 0)
'.LastName = Application.WorksheetFunction.VLookup(CLng(FRMLookup.passNum), Sheet2.Range("Lookup"), 2, 0)
'.DateIssued = Application.WorksheetFunction.VLookup(CLng(FRMLookup.passNum), Sheet2.Range("Lookup"), 4, 0)
'.Notes = Application.WorksheetFunction.VLookup(CLng(FRMLookup.passNum), Sheet2.Range("Lookup"), 8, 0)
' load the loop up range in to a variant array
lookuparr = Sheet2.Range("Lookup")
' loop through the array
For i = 1 To UBound(lookuparr)
' compare the first column of the array with the passnum
If lookuparr(i, 1) = FRMLookup.passNum Then
' match found so copy the variables
.PassRem = lookuparr(i, 7)
.FirstName = lookuparr(i, 3)
.LastName = lookuparr(i, 2)
.DateIssued = lookuparr(i, 4)
.Notes = lookuparr(i, 8)
' match foudn so exit loop
Exit For
End If
Next i
End With