I'm a bit confused here so just trying to understand what you are doing.
From what I understand 5.01 Lite was working OK, you upgraded this to 5.03 with your old hard drive connected that you use for the old version 4.xxx and I assume it worked and played OK.
Or am I understanding this wrong up to this point ?
When you first started this Hoster version 5.03 with your external drive plugged in it would have rebuilt the database to suit the extra database fields used in 5.03. Once this is done the songs.mdb can not be used in an earlier version.
Now you say when you try and add your kma files into the database
Are you trying to load more kma folders into version 5.03. or 4.xxx?
Are you trying to do this via the Build Database Add folder tab in 5.03 or by copying the songs.mbd as this last option won't be compatible.
What I mean by forward and backward compatible is you can use files created in 4.xxx and they will work in 5.03 but you can't use files created in 5.03 in version 4.xxx. to the best of my knowledge.
As to your other question, Yes the newer versions of Hoster support Indexing videos and mp3.