> AFAIS this hasn't nothing to do with DoubleBuffering. You have (ok, IBO
> has) a Font which is already 'nil' at destruction time. Hmmm... but
> unfortunately from where I'm typing I cannot look at the source now...
>
> m.th.

Then perhaps there is more than one problem here.

If I open a simple form with a TIB_Grid I can open the TIB_Query connected to the TIB_grid and it displays the data correctly. If I then close the query I get the error ...

exception number : 1
exception class : EAccessViolation
exception message : Access violation at address 004021C4 in module 'EngSys.exe'. Read of address 00000000.

main thread ($1724):
004021c4 +010 EngSys.exe System 31 +0 SysReallocMem
00403185 +00d EngSys.exe System 31 +0 @ReallocMem
0052d5cd +0a1 EngSys.exe Grids ModifyExtents
0052d630 +014 EngSys.exe Grids UpdateExtents
0052ff3c +054 EngSys.exe Grids DoChange
00530148 +0b8 EngSys.exe Grids TCustomGrid.ChangeSize
00532e1c +034 EngSys.exe Grids TCustomGrid.SetRowCount
005eff9f +283 EngSys.exe IB_Grid 3843 +40 TIB_CustomGrid.UpdateRowCount
005eef24 +03c EngSys.exe IB_Grid 3391 +6 TIB_CustomGrid.SysDataChange
005edc78 +008 EngSys.exe IB_Grid 76 +1 TIB_CustomGrid.DataChange
0058c4bd +019 EngSys.exe IB_Components 38248 +2 TIB_DataLink.DoDataChange
0058c365 +041 EngSys.exe IB_Components 38190 +5 TIB_DataLink.SysDataChange
005cea49 +005 EngSys.exe IB_FieldDataLink 367 +1 TIB_ControlDataLink.SysDataChange
0058cd5d +131 EngSys.exe IB_Components 38391 +11 TIB_DataLink.ProcessStatementEvent
0058ae18 +070 EngSys.exe IB_Components 37153 +23 TIB_DataSource.ProcessEvent
00569b74 +06c EngSys.exe IB_Components 23407 +7 TIB_Statement.ProcessLinkEvent
0057825f +077 EngSys.exe IB_Components 29507 +15 TIB_Dataset.ProcessLinkEvent
005679c5 +005 EngSys.exe IB_Components 22421 +1 TIB_Statement.SysAfterFieldDataChange
0057ba06 +016 EngSys.exe IB_Components 30972 +2 TIB_BDataset.SysAfterFieldDataChange
005924e1 +011 EngSys.exe IB_Components 40531 +2 TIB_Row.DoAfterModify
00592469 +011 EngSys.exe IB_Components 40489 +3 TIB_Row.SysAfterModify
00592210 +048 EngSys.exe IB_Components 40377 +10 TIB_Row.ClearBuffers
0057e048 +0a8 EngSys.exe IB_Components 32105 +18 TIB_BDataset.SysAfterClose
00570991 +215 EngSys.exe IB_Components 26135 +45 TIB_Dataset.SysClose
0056fc06 +092 EngSys.exe IB_Components 25772 +7 TIB_Dataset.Close
00573994 +020 EngSys.exe IB_Components 27302 +5 TIB_Dataset.SetActive
00880095 +059 EngSys.exe Countries_U 76 +13 TCountries.BtnExitClick
00502a8b +06f EngSys.exe Controls TControl.Click
004dd954 +000 EngSys.exe ComCtrls TToolButton.Click
00502efe +066 EngSys.exe Controls TControl.WMLButtonUp
00502522 +2d2 EngSys.exe Controls TControl.WndProc
00502148 +024 EngSys.exe Controls TControl.Perform
0050623a +0ae EngSys.exe Controls GetControlAtPos
00506302 +0a6 EngSys.exe Controls TWinControl.ControlAtPos
00502148 +024 EngSys.exe Controls TControl.Perform
005063b7 +097 EngSys.exe Controls TWinControl.IsControlMouseMsg
005068d2 +3be EngSys.exe Controls TWinControl.WndProc
004e2380 +244 EngSys.exe ComCtrls TToolBar.WndProc
00506140 +02c EngSys.exe Controls TWinControl.MainWndProc
0048835c +014 EngSys.exe Classes StdWndProc
00883b6e +022 EngSys.exe Start_U 198 +2 TStart.Countries1Click
004f6eff +0a7 EngSys.exe Menus TMenuItem.Click
004f81b3 +013 EngSys.exe Menus TMenu.DispatchCommand
0051f4b7 +01f EngSys.exe Forms TCustomForm.WMCommand
00502522 +2d2 EngSys.exe Controls TControl.WndProc
00506a27 +513 EngSys.exe Controls TWinControl.WndProc
0051c434 +594 EngSys.exe Forms TCustomForm.WndProc
00506140 +02c EngSys.exe Controls TWinControl.MainWndProc
0048835c +014 EngSys.exe Classes StdWndProc
7739490f +010 kernel32.dll BaseThreadInitThunk

I can then close that form but if I then close the application I get the same error message again (and again...!)

I don't really know whether this helps or confuses things!

Chris