Short reference pages on the errors and access problems that come up when you are moving files between servers or looking at an unfamiliar site. Each one explains what the response actually means before it gets to fixes.
Server responses
401 UnauthorizedAuthentication is missing or wrong
403 ForbiddenAuthenticated, but not permitted
406 Not AcceptableContent negotiation failed
413 Request Entity Too LargeUpload exceeds the server limit
Access and transfer
What is FTPAnd how to find your access details
SFTP in FileZillaConnecting over SFTP
Identifying a CMSWorking out what a site runs on
301 redirects in WordPressHow redirect handling works