Mp4 files not supported any more

I have Windows XP running on Sony Vegas and I needed the Klite Codec for importing MP4 files as I commonly get "None of the files dropped could be opened" message.
The Klite codec pack Used to work with mp4, and now it does not.
When I installed it again today Mp4 files still did not work.
I am wondering if this is because Apple's dropped support for Quicktime on Windows which is giving me great stress as I often use my Windows for video editing..
However after I installed it Some m4v files worked on Vegas, but not all, which is really weird.

Sony Vegas does not use DirectShow, so it won't use external codecs for importing MP4 or other stuff like MKV. The only kind of external codecs that it can use are VFW codecs, which are for AVI files.

It needs QuickTime for importing MP4 files. You can still use it even though Apple dropped support for it. You can customize its installation to only install the required parts and skip the isecure parts (browser plugin and player). Here is a tutorial:
http://codecguide.com/quicktime_installation.htm