What does "Invalid address specified to RtlFreeHeap( 06450000, 08387460 )" mean? - delphi

Question

Sometimes I experience random crashes in my Delphi program. My program halts, and the Debugger outputs:
Invalid address specified to RtlFreeHeap( 06450000, 08387460 )
What does that mean? And what can possibly cause it?
This is where the CPU Inspector stopped:
77BA0845 C6052582BD7700 mov byte ptr [$77bd8225],$00
Please note that they are very random (for me). Sometimes they don't appear at all.
I am using the Skype4COM.dll from Skype - there's no source though.
In case you need it, here is the code. I have commented most of the calls to Synchronize, so you know what they do.
////////////////////////////////////////////////////////////////////////////////
/// Execute
////////////////////////////////////////////////////////////////////////////////
procedure TContactDeletor.Execute;
Var
I : Integer;
UserObj : PUser;
User : IUser;
PauseEvent : TEvent;
begin
inherited;
FreeOnTerminate := True;
if Terminated then
Exit;
CoInitialize(Nil);
// The F-Flags are to make sure TSkype events do not fire (from my Main Thread)
FAllowUI := False;
FUserIsBeingDeleted := False;
FUseGroupUsersEvent := False;
FUseRenameEvent := False;
SkypeThr := TSkype.Create(Nil);
SkypeThr.Attach(10,False);
SkypeThr.Cache := False;
MyList := TStringList.Create;
PauseEvent := TEvent.Create(True);
try
// This fills my Stringlist
Synchronize(GrabList);
if Terminated then Exit;
iMax := MyList.Count;
// This sets the Max of my Progressbar
Synchronize(SetMax);
Try
for I := 0 to MyList.Count - 1 do
begin
{while SkypeThr.AttachmentStatus <> apiAttachSuccess do
begin
SkypeThr.Attach(10,False);
Synchronize(Procedure Begin Log('Skype Unavailable - Trying to reconnect ...'); End);
PauseEvent.WaitFor(5000);
end; }
CurUser := '';
User := SkypeThr.User[MyList[I]];
CurUser := MyList[I];
Try
User.IsAuthorized := False;
User.BuddyStatus := budDeletedFriend;
Except on E:Exception do
begin
ExErr := E.Message;
ExLog := 'Error while deleting contacts: ';
ExMsg := 'An Error has occured while deleting contacts: ';
Synchronize(
Procedure
Begin
Log(ExLog+ExErr+sLineBreak+' - Last logged Handle: '+CurUser);
End
);
end;
end;
iProgress := I+1;
// This updates my log and my progressbar.
Synchronize(UpdatePG);
PauseEvent.WaitFor(100);
if (I mod 200 = 0) and (I > 0) then
begin
// Calls to Synchronize updates my log
Synchronize(SyncPauseBegin);
PauseEvent.WaitFor(3000);
Synchronize(SyncPauseEnd);
end;
end;
// Except
Except on E:Exception do
begin
ExErr := E.Message;
ExLog := 'Error while deleting contacts: ';
ExMsg := 'An Error has occured while deleting contacts: ';
Synchronize(
Procedure
Begin
Log(ExMsg+ExErr+sLineBreak+' - Last logged Handle: '+CurUser);
ErrMsg(ExMsg+ExErr+sLineBreak+sLineBreak+' - Last logged Handle: '+CurUser);
End
);
Exit;
end;
end;
// This synchronizes my visual list.
Synchronize(SyncList);
finally
FUserIsBeingDeleted := False;
FUseGroupUsersEvent := True;
FUseRenameEvent := True;
FAllowUI := True;
Synchronize(
Procedure
Begin
frmMain.UpdateStatusBar;
PleaseWait(False);
ToggleUI(True);
end);
PauseEvent.Free;
SkypeThr.Free;
MyList.Free;
CoUninitialize;
end;
end;

Answer 1

Najem was correct, it is because your heap is corrupted. To debug it easier, you should enable PageHeap, also, use the debug CRT (or debug delphi runtime) as much as possiable until you find out what's corrupting your memory.
A lot of the time, the corruption may only spill over a few bytes. Then your application can run fine for a very long time, so you will not notice anything wrong until much later, if at all.
Try to exit your application cleanly when your looking for memory corruption bugs, dont just stop the debugger, when your process is exiting, it should "touch" most of the memory it allocated earlier and it will give you a chance to detect the failure.