Abstract Error when destroying Frames

Question

After discovering that we had some basic memory leaks I've been giving some of our applications a spring clean. After plugging FastMM4 into one of our applications I'm getting an abstract error that appears to be when I clear a list of frames

I have a Form with a scroll box on it. The scrollbox has either a list of results or details. The results and details are both designed in frames.

First I get a batch of results (upto 25 records) and create the appropriate # of frames

var
  Framelist: TList;
  NewSF: TSF;
begin
  Framelist := TList.Create;
  for i := 0 to Batch.Count - 1 do
  begin
    NewSF := TSF.Create(nil);
    NewSF.Name := 'SF' + IntToStr(i);
    NewSF.Parent := ScrollBox1;
    FrameList.Add(NewSF);
  end;
end;

When a frame is clicked on the result frames are clear and a detail frame created on the scrollbox in their place. I have currently deactivated the creation of the detail frame and am concentrating on clearing the frames.

The frames were initially being cleared like this:

while FrameList.Count > 0 do
begin
  TSF(FrameList[0]).free;
  FrameList.delete(0);
end;

I have also tried like this:

for i := 0 to FrameList.Count - 1 do
begin
  SF := FrameList[i];
  SF.Free;
  SF := nil;
end;

Any suggestions on what I am doing wrong - either on creation or destruction?