This wouldn't be a java error. When you launch the admin console you are talking to the Tomcat webs server built into FMS (runs on port 16000). The exceptions shows error 403 which is the web server saying: I'm here and I'm listening but I'm not allowed to give you the file you are looking for (the jar file). So it's a permissions error.
The fact that this happens every month is a good clue: what is running on your machine about every month that results in this? Automatic updates? Anything else on the machine (is the machine dedicated?)
Any disk ecnryption or AV running with on-demand scanning? Indexing? (basically anything that can put a OS-level readl block on the file).
Are you using "localhost" in the url? Try the IP address or DNS name of the machine, even if you are on the machine itself.