Parameter integrity error occurred with reason code 3

Hello.

I'm an MI newbie and having a problem using the OPEN instruction (v5r2).
Here is a simple code, for example: 

DCL DD RESOLVE CHAR(34);                                            
    DCL DD RESOLVE-TYPE CHAR( 2) DEF(RESOLVE) POS( 1);              
    DCL DD RESOLVE-NAME CHAR(30) DEF(RESOLVE) POS( 3);              
    DCL DD RESOLVE-AUTH CHAR( 2) DEF(RESOLVE) POS(33) INIT(X'0000');
DCL SYSPTR .SEPT(6440) BAS(SEPT-POINTER);                           
DCL SPC PROCESS-COMMUNICATION-OBJECT BASPCO;                        
    DCL SPCPTR SEPT-POINTER DIR;                                     
DCL DD INBUF   CHAR(35) BAS(.OFCB-INBUF);                          
DCL DD OUTBUF  CHAR(35) BAS(.OFCB-OUTBUF);                         

DCL SPCPTR .NULL;                              
ENTRY * EXT;                            

     CPYBLA       RESOLVE-TYPE, X'0201';                  
     CPYBLAP      RESOLVE-NAME, "SCRNIO", " ";          
     RSLVSP      .SCRNIO, RESOLVE, *, *;                  
                                                          
     CPYBLA       CTRL-OPCODE, "OPEN";                    
     CALLX       .SCRNIO, SCRNIO, *;     
/********************************************************************/ 
                                                                       
    CPYBLAP     OFCB-FILE,    "SOMEPF"," ";                           
    CPYBLAP     OFCB-LIBRARY, "*LIBL"," ";                             
    CPYBLAP     OFCB-MEMBER,  "*FIRST"," ";                            
    CPYNV       OFCB-RECORD-LENGTH,35;                                 
                                                                       
    CALLX      .SEPT(OPEN-ENTRY), OPEN-O, *;                           
BRK "1";                                                               
    CALLX      .SEPT(CLOSE-ENTRY), OPEN-O, *;                                   
        
    CPYBLA       CTRL-OPCODE, "CLOSE";          
    CALLX       .SCRNIO, SCRNIO, *;             
/********************************************************************/  
DCL SPCPTR .SCREEN INIT(SCREEN);                                        
DCL DD SCREEN CHAR(10) INIT("T010270005");                              
    DCL DD S-TITLE CHAR( 5) INIT ("Title");                                  
DCL DD * CHAR(10) INIT("L010520000");                                   
                                                                        
DCL SPCPTR .SCRN-CTRL INIT(SCRN-CTRL);                                  
DCL DD SCRN-CTRL CHAR(8);                                               
    DCL DD CTRL-OPCODE          CHAR(1) DEF(SCRN-CTRL) POS(1);          
    DCL DD CTRL-CMD-KEY        ZND(2,0) DEF(SCRN-CTRL) POS(2);          
    DCL DD CTRL-CURSOR-POSITION CHAR(5) DEF(SCRN-CTRL) POS(4);          
      DCL DD CTRL-CURSOR-ROW ZND(2,0) DEF(CTRL-CURSOR-POSITION) POS(1); 
      DCL DD CTRL-CURSOR-COL ZND(3,0) DEF(CTRL-CURSOR-POSITION) POS(3); 
                                                                        
DCL SYSPTR .SCRNIO;                                                     
DCL OL SCRNIO (.SCRN-CTRL, .SCREEN);                                    

DCL CON OPEN-ENTRY   BIN(2)   INIT(12);                      
DCL CON CLOSE-ENTRY  BIN(2)   INIT(11);       
               
DCL SPCPTR .OFCB INIT(OFCB);                                 
DCL DD OFCB CHAR(217) BDRY(16);                              
    DCL SPCPTR .OFCB-ODP               DEF(OFCB) POS(  1);   
    DCL SPCPTR .OFCB-INBUF             DEF(OFCB) POS( 17);   
    DCL SPCPTR .OFCB-OUTBUF            DEF(OFCB) POS( 33);   
    DCL DD OFCB-FILE          CHAR(10) DEF(OFCB) POS(129);            
    DCL DD OFCB-LIB-ID        BIN(2)   DEF(OFCB) POS(139) INIT(72);   
    DCL DD OFCB-LIBRARY       CHAR(10) DEF(OFCB) POS(141);            
    DCL DD OFCB-MBR-ID        BIN(2)   DEF(OFCB) POS(151) INIT(73);   
    DCL DD OFCB-MEMBER        CHAR(10) DEF(OFCB) POS(153);            
    DCL DD OFCB-FLAGS-1       CHAR(1)  DEF(OFCB) POS(175) INIT(X'80');
    DCL DD OFCB-FLAGS-2       CHAR(1)  DEF(OFCB) POS(176) INIT(X'3C');
    DCL DD OFCB-RECORD-ID     BIN(2)  DEF(OFCB) POS(209) INIT(1);     
    DCL DD OFCB-RECORD-LENGTH  BIN(2)   DEF(OFCB) POS(211);           
    DCL DD OFCB-LEVEL-ID       BIN(2)   DEF(OFCB) POS(213) INIT(6);    
    DCL DD OFCB-LEVEL-NO      CHAR(1)   DEF(OFCB) POS(215) INIT(X'00');
    DCL DD OFCB-NO-MORE-PARMS BIN(2)  DEF(OFCB) POS(216) INIT(32767);  
 DCL OL  OPEN-O(.OFCB);                                                 
DCL OL CLOSE-O(.OFCB);                                                 
                                                                       
PEND;                                                                  

The SCRNIO programm is straight from Leif's MI examples.  

When I call my program from a command line straight after SIGNON I get no 
errors, but sometimes I get (especially when i call other programs before):
Message ID . . . . . . :   CPF411D
Parameter integrity error occurred with reason code 1.    
    1 -- A pointer was used that is not available for use while running in the 
current program state.                          
                                                                           
And sometimes:
Parameter integrity error occurred with reason code 3.    
3 -- A pointer type was not valid for the requested operation.     

The instruction is
CALLX      .SEPT(OPEN-ENTRY), OPEN-O, *;    

I'm missing something simple here...but just can't see it...
Any help would be appreciated :)