> Have you looked in the firebird.log/interbase.log to see whether

there's anything interesting there?

Thanks Helen.

There is nothing interesting in the firebird.log.
However here are the further details of the error message:

+ $12C[11FF6930]{IBO40CRT_D2006.bpl}
Ib_components.TIB_Statement.CheckConnection + $12C
+ $D[11FF6BE1]{IBO40CRT_D2006.bpl}
Ib_components.TIB_Statement.SysAllocate + $D
+ $1A[124827E6]{IBO40XRT_D2006.bpl}
Ibodataset.TIBODataset.DoBeforeOpen + $1A
+ $13[055CEABF]{dbrtl100.bpl} DB.DB.TDataSet.Loaded (Line 9084,
"DB.pas" + 3) + $13
+ $18[1247EE74]{IBO40XRT_D2006.bpl} Ibodataset.TIBODataset.Loaded + $18
+ $B[51F50AE4]{rtl100.bpl } Classes.Classes.NotifyGlobalLoading
(Line 2681, "classes.pas" + 3) + $B
+ $6[20F181E2]{designide100.bpl}
ComponentDesigner.ComponentDesigner.TComponentRoot.Create (Line 2117,
"ComponentDesigner.pas" + 33) + $6
+ $27[0962B5B9]{delphivclide100.bpl}
VCLFormDesigner.VCLFormDesigner.TVCLFormDesigner.CreateRoot (Line
1271, "VCLFormDesigner.pas" + 3) + $27
+ $8A[21C13627]{delphicoreide100.bpl}
DelphiModule.DelphiModule.TPascalCodeMgrModHandler.SetupSourceModules
(Line 545, "DelphiModule.pas" + 67) + $8A
+ $7[21C12FBA]{delphicoreide100.bpl}
DelphiModule.DelphiModule.TPascalCodeMgrModHandler.Create (Line 437,
"DelphiModule.pas" + 4) + $7
+ $16[21C19191]{delphicoreide100.bpl}
DelphiModule.DelphiModule.TPascalGauntletHandler.AttachHandler (Line
2514, "DelphiModule.pas" + 6) + $16
+ $1E[20C3B629]{coreide100.bpl}
DocModul.DocModul.TModuleHandlerGauntlet.RunGauntlet (Line 3019,
"DocModul.pas" + 4) + $1E
+ $7[20C3708E]{coreide100.bpl}
DocModul.DocModul.TDocModule.AfterConstruction (Line 910,
"DocModul.pas" + 4) + $7
+ $5[51F269D1]{rtl100.bpl } System.System.@AfterConstruction (Line
9537, "system.pas" + 2) + $5
+ $25[20BAFAB8]{coreide100.bpl}
SourceModule.SourceModule.TSourceModule.Create (Line 347,
"SourceModule.pas" + 6) + $25
+ $D[20BB33B4]{coreide100.bpl}
SourceModule.SourceModule.TSourceModuleFormHandler.CreateModule (Line
1577, "SourceModule.pas" + 1) + $D
+ $E[20BB9D7C]{coreide100.bpl}
Desktop.Desktop.TDesktopFormHandlers.DoCreateModule (Line 259,
"Desktop.pas" + 6) + $E
+ $12[20BBAEDE]{coreide100.bpl} Desktop.Desktop.LoadDeskFile (Line
727, "Desktop.pas" + 30) + $12
+ $1F[20BBC2CC]{coreide100.bpl} Desktop.Desktop.LoadProjectDesktop
(Line 1079, "Desktop.pas" + 8) + $1F
+ $2[20BACDC8]{coreide100.bpl}
ProjectFileUtils.ProjectFileUtils.ShowProject (Line 609,
"ProjectFileUtils.pas" + 8) + $2
+ $4[20C041EE]{coreide100.bpl}
ProjectGroup.ProjectGroup.TProjectGroupFormHandler.OpenModule (Line
2716, "ProjectGroup.pas" + 6) + $4
+ $B[20B5EA9D]{coreide100.bpl} FileHist.FileHist.TClosedFile.Open
(Line 123, "FileHist.pas" + 7) + $B
+ $7[51F5FEFF]{rtl100.bpl } Classes.Classes.TBasicAction.Execute
(Line 11070, "classes.pas" + 3) + $7
+ $3[218BD460]{vclactnband100.bpl}
ActnMenus.ActnMenus.TCustomActionMainMenuBar.TrackMenu (Line 3143,
"ActnMenus.pas" + 3) + $3
+ $4[218B891D]{vclactnband100.bpl}
ActnMenus.ActnMenus.TCustomActionMenuBar.CMItemClicked (Line 883,
"ActnMenus.pas" + 3) + $4
+ $6[5205CA19]{vcl100.bpl } Controls.Controls.TWinControl.WndProc
(Line 7246, "Controls.pas" + 105) + $6
+ $4[218BA158]{vclactnband100.bpl}
ActnMenus.ActnMenus.TCustomActionMenuBar.WndProc (Line 1572,
"ActnMenus.pas" + 15) + $4
+ $0[51F60BC0]{rtl100.bpl } Classes.Classes.StdWndProc (Line 11572,
"classes.pas" + 8) + $0
+ $6A[7E418731]{USER32.dll } GetDC + $6A
+ $14A[7E418811]{USER32.dll } GetDC + $14A
+ $122[7E4189C8]{USER32.dll } GetWindowLongW + $122
+ $A[7E4196C2]{USER32.dll } DispatchMessageA + $A