7.3 defaults to SMB2 rather than SMB1, so I'd wager that's your problem.  The quick-and-dirty fix is to disable SMB2, although I wouldn't recommend that.  
We had a similar problem with our 7.1->7.3 upgrade.  For us the issue was password case.  The Windows password was mixed case.  With 7.1 (SMB1) and password level 0 it worked.  At 7.3 (SMB2) it didn't.  We changed the password level and made the passwords fully match.
HTH
-----Original Message-----
From: Tom Deskevich [mailto:TDeskevich@xxxxxxxxxxxxxxxxxx] 
Sent: Saturday, February 02, 2019 5:50 AM
To: midrange-l@xxxxxxxxxxxxxxxxxx
Subject: Security errors on image server via QNTC.
   We just migrated from one Power box to another. 
   On the old box, you can drill in via QNTC to the image server and copy,
   delete rename images.
   On the new box, you get security errors, using the same credentials.
   You can see the directory via QNTC on the new box, but not update
   anything. 
   So it appears it is initially OK with the credentials passed. 
   The password levels are the same.(0)
   The SMB levels are the same.
   Our IT tech tells us PTFs are current on the new box.
   Old box was on 7.2 new one on 7.3
   We have a ticket with IBM, with no response yet. Just wondering if YINZ
   can help.
   Message ID . . . . . . :   CPFA09C       Severity . . . . . . . :   40   
        
   Message type . . . . . :   Diagnostic                                     
       
   Date sent  . . . . . . :   02/02/19      Time sent  . . . . . . : 
    06:39:02   
                                                                            
        
   Message . . . . :   Not authorized to object.  Object is                 
        
     /qntc/<server name>/2019/faacgnvh.xxx.                                 
      
   Cause . . . . . :   You do not have the correct authority for object     
        
     /qntc/<>/erirod/2019/faacgnvh.xxx or for one of the directories in the 
     object path.                                                           
        
   Recovery  . . . :   Contact your security officer, the object owner, or
   other  
     authorized person to obtain the correct authority to use object         
       
     /qntc/<>/erirod/2019/faacgnvh.xxx or the directories in the object     
     path, and try your request again. If the object name is *N, it could not
   be  
     determined which of the objects authority was not sufficient.           
       
       The Security Reference, SC41-5302, contains authority information for
   the  
   Dump that our IT guy gave me on SMB
   Old system
       
   RID                                                                                          
   02/01/19  10:26:43   PAGE 
   LIC LOG ENTRY ID 0100927F  TYPE 4400 (SERVER MSG BLK  ) F001  NOTE SIZE
   0068  DUMP SIZE 0000E6  TIME STAMP 02/01/19  10:26:43
   REQUESTER TDE:B000600002 A2C000   NAME:SK-ASC051P                    
   LINKREG:FFFFFFFFC6 3D14D8                              
        RID                                               ZLS EXTENSION
   FLAGS                         02/01/19  10:26:43   PAGE 
   DUMP FOR ENTRY ID 0100927F TYPE 4400 (SERVER MSG BLK  ) F001  DUMP SIZE
   0000E6  TIME STAMP 02/01/19  10:26:43                
   OLD
   FLAGS                                                                                                
                       
   0000000000000000                                                                                                             
   NEW
   FLAGS                                                                                                  
                     
   0000000000000000                                                                                                             
   ****** END OF DUMP
   ******                                                                                    
                   
   New System
       
   RID                                                                                          
   02/01/19  10:30:52   PAGE
   LIC LOG ENTRY ID 01000290  TYPE 4400 (SERVER MSG BLK  ) F001  NOTE SIZE
   0068  DUMP SIZE 0000E8  TIME STAMP 02/01/19  10:30:52
   REQUESTER TDE:B000B00001 C48000   NAME:SK-ASC051P                    
   LINKREG:FFFFFFFFC7 989C98                             
        RID                                               ZLS EXTENSION
   FLAGS                         02/01/19  10:30:52   PAGE
   DUMP FOR ENTRY ID 01000290 TYPE 4400 (SERVER MSG BLK  ) F001  DUMP SIZE
   0000E8  TIME STAMP 02/01/19  10:30:52               
   OLD
   FLAGS                                                                                                                
      
   0000000000000000                                                                                                            
   NEW
   FLAGS                                                                                                                   
   0000000000000000                                                                                                            
   ****** END OF DUMP ******                                                 
                                                     
   Harriscomputer
   Tom Deskevich
   Programmer/Analyst                             172 Gateway Road PO Box 568
                                                      Ebensburg, Pennsylvania
   P: 814-472-6066 x134                                                 15931
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