I am sorry but my experiences are same about 503 errors. It is rondom, sometimes people get 503 error, somtimes blank pages. Is there a link to download older versions like 4.0.4? There was no problem with this version.
BTW I really want to undersand the reason. For example what causes to "Max retries has been reached, 503!". May be there can is a configuration issue. I really need urgent help...