MP4 Does not appear in WMP11 Library?

I am unable to get WMP11 on Vista to import and, display in the
library, MP4 files created using Nero Recode set to encode to AVC.
WMP11 is able to play the MP4 video just fine, I've installed the Zune
softward thinking that this may have fixed the problem as it has built
in support for AVC/MPEG4. My feeling is that it's something to do
with containers becuase the codec seems to be ok. Any help would be
most appreciated as I'm not very knowledge in this area.

Thanks,

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