Your script contains an error. Missing endif.
Some remarks:

• we think your meaning with line
  IF @wksta <> 'test-a' AND @wksta <> 'test-b' AND @wksta <> 'test-c' AND @wksta <> sfu1-018
  is: run script test.scr when workstation name is one of those names.
  YES: change it to
  @wksta = 'test-a' OR @wksta = 'test-b' OR @wksta = 'test-c' OR @wksta = sfu1-018
  
• same remark about your line IF @wksta <> 'preprod-a' AND @wksta <> 'preprod-b'
  change it to IF @wksta = 'preprod-a' OR @wksta = 'preprod-b'
  
• use MessageBox instead of ? 'Press any key to continue...'.
  You doesn't need the BEEP command by using the MessageBox function.
  

We verify your code with our tool kixstrip.
Result:

code:

---

 IF @wksta <> 'test-a' AND @wksta <> 'test-b' AND @wksta <> 'test-c' AND @wksta <> sfu1-018
       CALL Test.scr
       $process_login='n'
       ?'Dublin Login scripts are NOT run on Test Machines.'
       ?
       BEEP
       BEEP
       ?'Press any key to continue...'
       IF @wksta <> 'preprod-a' AND @wksta <> 'preprod-b'
             CALL Preprod.scr
             $process_login='n'
             ?'Dublin Login scripts are NOT run on Pre-Production Machines.'
             ?
             BEEP
             BEEP
             ?'Press any key to continue...'
       ELSE 
             IF exist ('c:\winnt\canflag.txt')=1
                   $process_login='n'
                   ?'Dublin Login scripts are NOT run on Canada Machines.'
                   ?' Please call 4500 for more info.'
                   ?
                   BEEP
                   BEEP
                   ?'Press any key to continue...'
                   GET $t
             ELSE
                   $process_login='y'
             ENDIF 
             ; if on nala
             IF $process_logon='y'
                   ?
                   ?'Processing NT system logon script...'
;($begin)
;
;                       fri 26-oct-2001 00:25:49       (kix 4.00 vs 2.29e)
;
;Informative KIXSTRIP:      input=32 output=32 skip=0
;
;Warning     KIXSTRIP:    1 error in block structure. missing statement(s).
;                           - do:until                 [0:0]
;                           - for|each:in|to:step|next [0|0:0|0:0|0]
;                           - function:endfunction     [0:0]
;                   -ERROR- - if:else:endif            [4:2:1]
;                           - select:case:endselect    [0:0:0]
;                           - while:loop               [0:0]
;Warning     KIXSTRIP: some lines contains errors or possible errors.
;Informative KIXSTRIP:    4 block_structures found.
;Informative KIXSTRIP:   no UDF's found.
;Informative KIXSTRIP:   no labels found.
;Summary     KIXSTRIP:      BREAK CALL DEBUG DISPLAY ENDFUNCTION EXECUTE EXIT FUNCTION GET GETS GOSUB GOTO OLExxx PLAY QUIT RETURN RUN SHELL SLEEP THEN USE
;Informative KIXSTRIP:    2 CALL
;Informative KIXSTRIP:    1 GET
;
;($end)

---

We restyle your script a little bit.
Our version is:

code:

---

$process_login="y"
SELECT
CASE (@wksta = "test-a") OR (@wksta = "test-b") OR (@wksta = "test-c") OR (@wksta = "sfu1-018")
  CALL test.scr
  $process_login="n"
  $result=MessageBox("Dublin Login scripts are NOT run on Test Machines.","Login process",16,30)
CASE (@wksta = "preprod-a") OR (@wksta = "preprod-b")
  CALL preprod.scr
  $process_login="n"
  $result=MessageBox("Dublin Login scripts are NOT run on Pre-Production Machines.","Login process",16,30)
CASE 1 
  IF (Exist("c:\winnt\canflag.txt") = 1)
    $process_login="n"
    $result=MessageBox("Dublin Login scripts are NOT run on Canada Machines."+CHR(13)+" Please call 4500 for more info.","Login process",16,30)
  ELSE
    $process_login="y"
  ENDIF
ENDSELECT
IF ($process_logon = "y")
  ? "Processing NT system logon script..."
ENDIF

---