Characters come and go, but History remembers them.
Until there are too many and it locks up.

Delete your old scrap characters.

Go to the savedvariables folder and copy the history.lua file somewhere safe.
The script makes a backup into a subfolder History_bak. You can totally trust that, Right?!  Nope.

Start the iuplua53.exe  console
Use the "Load" button, navigate to the history folder and select  Delete-Character.lua
Click Execute.

If there is more than one account in use, select the account.

Make the dialog wider, because I can't be arsed figuring out how to do it under program control.

Select a Character to be deleted.

Click "Execute" again to delete another char and repeat.

Close the iuplua console when finished.