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Please also Cc the port's maintainer.
You may be thinking of #31073, a general problem fetching from version control systems including CVS, which was introduced in MacPorts 2.0.2 an fixed in MacPorts 2.0.3. That problem had produced the strange error message " does not exist in". The error you are experiencing here is a different error: "CVS login failed". The log elaborates: "connect to common-lisp.net(74.115.254.14):2401 failed: Operation timed out". I am able to fetch slime just fine right now. Can you clean and try again to verify it was not just a temporary problem with their server?
sudo port clean slime
If that does not work, are you on a corporate or otherwise restricted network that might be blocking access to CVS's port 2401? Try accessing other CVS servers, or ask your network administrators if you don't know.