Offending code (in RTBC_ModManager.cs):
%zip = getSubStr(%filepath,0,strPos(%filepath,"/description.txt"))@".zip";
strPos is case sensitive and a bunch of your files have a Description.txt - I can't remember if there's a stripos function but if there is then this is your solution:
%zip = getSubStr(%filepath,0,striPos(%filepath,"/description.txt"))@".zip";
Otherwise this:
%zip = getSubStr(%filepath,0,strPos(strlwr(%filepath),"/description.txt"))@".zip";