I don't understand why I'm getting EAccessViolation. This happens when closing my application.

I don't understand why I'm getting EAccessViolation. This happens when closing my application.

I'm basically displaying frames. I'm calling a "Start" method after displaying them.

procedure TfrPicpic.Start;
begin
if Assigned(AnonymousThread) then
AnonymousThread.Terminate;

pnDeviceNotReachable.Visible := false;
pnDeviceNotReachable.Align := alNone;
AnonymousThread := TThread.CreateAnonymousThread(
procedure()
var
isopen: boolean;
begin

while not AnonymousThread.CheckTerminated do
begin
if Assigned(Connection) then
isopen := PortIsOpen(5432, Connection.Server);

AnonymousThread.Synchronize(nil,
procedure()
begin
if not isopen and Assigned(pnPicpicEteinds) then
begin
pnDeviceNotReachable.Align := alClient;
pnDeviceNotReachable.Visible := true;
end
else
begin
pnDeviceNotReachable.Visible := false;
pnDeviceNotReachable.Align := alNone;
end;
end);
sleep(500);
end;
end);

AnonymousThread.Priority := tpLower;
AnonymousThread.FreeOnTerminate := false;
AnonymousThread.Start;
end;


Prior destroying them, I'm calling the "Stop" method :

procedure TfrPicpic.Stop;
begin
if Assigned(AnonymousThread) then
AnonymousThread.Terminate;
end;

destructor TfrPicpic.Destroy;
begin
stop;
inherited;
end;

What's going wrong ?