Have you tried to convert another map? I can only repeat, what was already said: Install UTMapConverter to UT99 and NOT to any Unreal version. Copy your map into your UT99 map folder! When the program can't find the file, you get a "failed to load level none.mylevel" and a "failed to find level ..." log (like in your screenshot).
I did install the map converter into UT, though, and I still get the same errors as before.
Converting other maps works, too.
Abandon the converter at all.
Export the map to T3D.
Load all packages it's supposed to use in UnrealEd for Unreal 224.
Import the map.
Voila, all references to stuff you forgot to load or chose not to will be set to null.
I tried that, but UPak is still in the map, and then textures and coronas are all messed up. The filesize does get reduced by a lot, though.