I tested it many times and there was really a problem with the jar file that getjar.com provided to the users. They seem to be editing the manifest file (where an important application property was being stored) and removing any parameter that's not standard, thus provoking an error ("java.lang.IllegalArgumentException: Null URL") when MIDlog tries to access the Internet via HTTP.
I changed the source code, hardcoding the app property into the MIDlog source, and that solved the problem. Now you can download MIDlog from Rawsocket site (http://rawsocket.org/midlog.wml) and from wap.getjar.com and they will both work perfectly.