Well as I see it he did take Shawn's advice and use an If Exist.

However if his original statement is correct about not wanting the file to copy if it does not exist then his code is still wrong as it will copy. If on the other hand you don't want the file to copy if it is not found in the first place then Kent's code is smaller and more efficient for the task.

If InGroup("Domain\Busers") ; If user is not in group abort this section of code 
  If Exist("c:\accapps\bps_0506.adp") ; If the file exists do more checking otherwise abort 
    $Result = CompareFileTimes("x:\apps\accapps\05-06\bps_0506.adp", "c:\accapps\bps_0506.adp")
    If $Result = 1 ; If compared file on server is newer copy to client 
      Copy "x:\apps\accapps\05-06\bps_0506.adp" "c:\accapps\bps_0506.adp"
    EndIf
  Else ; File was not found so copy it 
    Copy "x:\apps\accapps\05-06\bps_0506.adp" "c:\accapps\bps_0506.adp"
  EndIf
EndIf