MPEG-4 v3 codec vanished from list of choices (suddenly)

I often use Microsoft's old MPEG-4 v3 in my WMV files that I have stored on
my HD. I just like the quality and vbr size to them.

But now all of a sudden, both the ISO MPEG-4 v1 and MPEG-4 v3 have
completely vanished from the list of available codecs. I'm using a program
that can access all of the available video/audio codecs on your system for
coding (i.e. Sony SoundForge).

When I attempt to run some of my other MPEG-4 v3 coded files, they run just
fine. When I load VirtualDub, I can clearly see the MPEG-4 codecs v1, v2 and
v3. But I'm not getting them as an option in the drop-down menus to create
WMV files.

These never used to be locked before and were always available for WMV (ASF)
files. So what's wrong with this? Why aren't these codecs showing up to be
used and can I list or tag them somehow to show up in the list of available
WMV codecs?

Thanks!