The Blitz IDE crashes when I close it (or close a tab).You need to update your Comctl32 setup. Comctl32 is the 'Common Control' library, which handles some of Windows' GUI components such as tabs and tree lists. You can update Comctl32 in one of two ways:
1) Install Internet Explorer 5 or above, or;
2) Download and run Microsoft's Comctl32 Installer from here (correct at the time of writing). Choose the latest x86 version. (The filename at the time of writing is '50comupd.exe'.)
Be aware that Comctl32 is an important update, so you should back up any important work before upgrading!