Error message when removing keys

I get this error message when I add/take off keys for tables - not sure why, can anyone help?

date/time : 2015-10-01, 09:21:42, 20ms
computer name : ______-Virt
user name : ______ <admin>
operating system : Windows XP Service Pack 3 build 2600
system language : English
system up time : 35 minutes 37 seconds
program up time : 15 minutes 23 seconds
processor : Intel(R) Pentium(R) 4 CPU 2.40GHz
physical memory : 7282/8095 MB (free/total)
free disk space : (C:) 146.66 GB
display mode : 1920x1080, 32 bit
process id : $24
allocated memory : 48.68 MB
largest free block : 251.37 MB
executable : heidisql.exe
exec. date/time : 2015-08-08 17:43
version : 9.3.0.4984
compiled with : Delphi XE5
madExcept version : 4.0.8.1
callstack crc : $3bd73f5e, $a0ab2f53, $a0ab2f53
exception number : 13
exception class : EAccessViolation
exception message : Access violation at address 0071D627 in module 'heidisql.exe'. Write of address 00730069.

main thread ($25):
0071d627 heidisql.exe VirtualTrees 28288 +7 TBaseVirtualTree.GetNodeData
0095e3b9 heidisql.exe Main 7675 +7 TMainForm.DBtreeInitNode
0070fbab heidisql.exe VirtualTrees 20191 +2 TBaseVirtualTree.DoInitNode
00713ef9 heidisql.exe VirtualTrees 22648 +10 TBaseVirtualTree.InitNode
0071b214 heidisql.exe VirtualTrees 26591 +6 TBaseVirtualTree.GetDisplayRect
0071eff7 heidisql.exe VirtualTrees 29439 +3 TBaseVirtualTree.InvalidateNode
007275fb heidisql.exe VirtualTrees 34134 +1 TCustomVirtualStringTree.InvalidateNode
0070f3cb heidisql.exe VirtualTrees 19785 +29 TBaseVirtualTree.DoFocusNode
007138fc heidisql.exe VirtualTrees 22457 +242 TBaseVirtualTree.HandleMouseDown
0070b11c heidisql.exe VirtualTrees 17178 +6 TBaseVirtualTree.WMLButtonDown
007189c8 heidisql.exe VirtualTrees 25260 +19 TBaseVirtualTree.WndProc
005b4138 heidisql.exe Vcl.Controls TWinControl.MainWndProc
0053b624 heidisql.exe System.Classes StdWndProc
7e9b7420 user32.dll DispatchMessageW
0068512f heidisql.exe Vcl.Forms TApplication.ProcessMessage
00685172 heidisql.exe Vcl.Forms TApplication.HandleMessage
006854ad heidisql.exe Vcl.Forms TApplication.Run
009819cb heidisql.exe heidisql 78 +24 initialization
7bc7c938 ntdll.dll RtlCaptureStackBackTrace

Many thanks!