This code in ThisWindow.Init can cause the 
 Assertion error, after a random number of 
 times opening the window. It does not matter 
 where I put the UNHIDE, here or in 
 ThisWindow.Open PROCEDURE 
 after Parent.Open
 or in 
 ThisWindow.TakeWindowEvent PROCEDURE
  OF EVENT:OpenWindow

 If I comment out my real estate code i.e.
 resizing window or creating controls or
 hiding some controls, it makes no difference.
 The assertion error can come even after 50
 times opening the window with no errors, and
 sometimes the second or third time the window
 is opened.
 
ThisWindow.Init PROCEDURE
  After 
  CLEAR(GlobalRequest)       
  CLEAR(GlobalResponse)

  SELF.Open(Wind10)    
  
   HIDE(0) 
   MenuStyleMgr.Init(?MENUBAR1)             
   MenuStyleMgr.SuspendRefresh()
   MenuStyleMgr.SetThemeColors('AutoNoBar')         
   MenuStyleMgr.SetImageBar(False)
   MenuStyleMgr.ApplyTheme()
   UNHIDE(0)   

 The UNHIDE can cause the assertion error.
 I have only five procedures with a menubar.
 Each procedure is called from an SDI window,
 and only gives the error if we START it on a thread.
 Here is a Window definition.

Wind10  WINDOW('..'),AT(,,400,260),FONT('Arial',9,,FONT:regular,CHARSET:DEFAULT),AUTO,CENTER, |
          ICON('Checkit.ICO'),MAX,STATUS(-1,80,120,45),SYSTEM
          MENUBAR,USE(?MENUBAR1),#ORDINAL(1)
            MENU('..File'),USE(?MFiles),#ORDINAL(2)
              ITEM('.'),USE(?TestAll),#ORDINAL(3)
              ITEM('Currency'),USE(?Currency),#ORDINAL(4)
              ITEM('Mark'),USE(?Markers),#ORDINAL(5)
              ITEM('Town'),USE(?TownCity),#ORDINAL(6)
              ITEM,USE(?Sep2),SEPARATOR,#ORDINAL(7)
              ITEM('.'),USE(?EmptyN),#ORDINAL(8)
              ITEM('.'),USE(?EmptyS),#ORDINAL(9)
            END
            ITEM('.'),USE(?PreSet),#ORDINAL(10)
            ITEM('.'),USE(?BackOrders),HIDE,#ORDINAL(11)
            MENU('..PC-data'),USE(?PCData),#ORDINAL(12)
              ITEM('PC data'),USE(?VolInfo),#ORDINAL(13)
              ITEM('IP='),USE(?IPAddy),#ORDINAL(14)
              ITEM('.'),USE(?Tester),#ORDINAL(15)
              ITEM('.'),USE(?Pather),#ORDINAL(16)
              ITEM('.'),USE(?Memoir),#ORDINAL(17)
              ITEM('.'),USE(?GetRec),#ORDINAL(18)
            END
            MENU('..Windows'),USE(?Windows),#ORDINAL(19)
              ITEM('Threads'),USE(?Threads),#ORDINAL(20)
              ITEM('Speed Test'),USE(?SpeedTest),#ORDINAL(21)
              ITEM('.'),USE(?pTimer),#ORDINAL(22)
            END
            ITEM('..'),USE(?Messaging),#ORDINAL(23)
            MENU('..Help'),USE(?Helper),#ORDINAL(24)
              ITEM('...'),USE(?LastPrint),#ORDINAL(25)
              ITEM('About'),USE(?About),#ORDINAL(26)
              ITEM('Offline Web pages'),USE(?WebPage),#ORDINAL(27)
              ITEM('See Changes'),USE(?SeeChanges),#ORDINAL(28)
              ITEM('Notice'),USE(?SeeWelcome),#ORDINAL(29)
              ITEM('Remote Desktop'),USE(?RDesktop),#ORDINAL(30)
              ITEM('How to Set Access'),USE(?HowSetAccess),#ORDINAL(31)
              ITEM('Import Excel'),USE(?ImportExcel),#ORDINAL(32)
              ITEM('Backup'),USE(?HowBackup),#ORDINAL(33)
              ITEM('M/F Costing'),USE(?MFcosting),#ORDINAL(34)
              ITEM('Markup'),USE(?SeeMarkup),#ORDINAL(35)
              ITEM('Gross profit'),USE(?SeeGrossP),#ORDINAL(36)
              ITEM('VAT'),USE(?VatDetails),#ORDINAL(37)
              ITEM('...'),USE(?IconListA),#ORDINAL(38)
            END
            ITEM,USE(?BranchUser),#ORDINAL(39)
            ITEM,USE(?FocusMain),#ORDINAL(40)
          END
          REGION,AT(134,63,21,171),USE(?RegWind),HIDE,IMM,#ORDINAL(41)
          BOX,AT(0,0,400,258),USE(?Wallpap),LINEWIDTH(1),#ORDINAL(42)
          LIST,AT(6,27,89,222),USE(?ListT),FORMAT('320L*I@s80@'),FROM(QuT),#ORDINAL(43)
          SHEET,AT(99,84),USE(?Sheet),FULL,HIDE,#ORDINAL(44)
            TAB,USE(?TabWind),#ORDINAL(45)
            END
          END
          GROUP,USE(?Group1),#ORDINAL(46)
            ENTRY(@s20),AT(106,68,75,11),USE(Finder),#ORDINAL(47)
            BUTTON,AT(183,63,19,18),USE(?ButKyb),#ORDINAL(48)
            BUTTON,AT(245,50,13,12),USE(?BMemo),#ORDINAL(49)
            LIST,AT(99,100),USE(?ListY),FULL,FROM(QuY),#ORDINAL(50)
            BUTTON,AT(137,49,58,14),USE(?Cancel),KEY(AltEsc),HIDE,#ORDINAL(51)
          END
          CHECK,AT(106,27,12,10),USE(Opt:hideclosedcr),VALUE('1','0'),#ORDINAL(80)
          STRING(@S40),AT(132,30,67,9),USE(OUA:Str35),#ORDINAL(81)
          CHECK,AT(200,27,12,10),USE(Opt:memorsupp),VALUE('1','0'),#ORDINAL(82)
          STRING(@S40),AT(214,30,73,9),USE(OUA:Str44),#ORDINAL(83)
          BOX,AT(92,18,98,50),USE(?BoxLicensee),HIDE,LINEWIDTH(1),ROUND,#ORDINAL(84)
          PROMPT('Int'),AT(94,16,94,32),USE(?Licensee),HIDE,#ORDINAL(85)
          BOX,AT(244,18,154,62),USE(?BoxTRHS),HIDE,LINEWIDTH(1),ROUND,#ORDINAL(86)
          STRING(@S40),AT(249,20,150,9),USE(QuY:Dis09),#ORDINAL(87)
          STRING(@S40),AT(249,29,150,9),USE(QuY:Dis10),#ORDINAL(88)
          STRING(@S40),AT(249,38,150,9),USE(QuY:Dis11),#ORDINAL(89)
          STRING(@S40),AT(249,47,150,9),USE(QuY:Dis12),#ORDINAL(90)
          STRING(@S40),AT(249,56,150,9),USE(QuY:Dis13),#ORDINAL(91)
          STRING(@S40),AT(249,65,150,9),USE(QuY:Dis14),#ORDINAL(92)
          STRING('Sting33'),AT(179,20,50,11),USE(?Sting33),HIDE,#ORDINAL(93)
          STRING(@n7),AT(20,200,12,10),USE(Aqu:acounst),HIDE,#ORDINAL(94)
          BUTTON,AT(306,220,50,14),USE(?Breaker),KEY(AltEsc),HIDE,#ORDINAL(95)
          STRING(@S50),AT(139,65,200,9),USE(QuY:Dis16),HIDE,#ORDINAL(96)
          STRING(@s40),AT(120,80,60,20),USE(OUA:Str71),HIDE,#ORDINAL(97) 
        END