There's no "DNS 305" error that I'm aware of; the DNS error
codes are all at most in the low double digits.
There is, however, an HTTP 305 error code. It means that you're
trying to access a URL directly and the webserver thinks you should
be accessing it through a proxy instead. Browsers are supposed to
intercept this and redirect to the proxy site automatically; if
you're seeing one (and you're not a webmaster looking at logs) then
it's a good bet that the website is messed up and there's not a lot
you can do about it.
If you're the webmaster, check your redirect and make sure it's
pointing at a valid server (that doesn't immediately try to
redirect back to you).