Problem:

Setup a FTP site allowing anonymous log in and with virtual host names enabled on Windows Server 2008 R2:

But when trying to connect to that FTP site with the user name anonymous, the following error was met:

Status:	Resolving address of test.com
Status:	Connecting to 10.43.41.22:21...
Status:	Connection established, waiting for welcome message...
Response:	220 Microsoft FTP Service
Command:	USER anonymous
Response:	331 Valid hostname is expected.
Command:	PASS **************
Response:	503 Login with USER first.
Error:	Critical error
Error:	Could not connect to server

Solution:

Prepend the virtual host name prior to the user name, and separate them with a pipe “|”, for example, ftp.test.com|anonymous. Then the log in process will be success.

Status:	Resolving address of test.com
Status:	Connecting to 10.43.41.22:21...
Status:	Connection established, waiting for welcome message...
Response:	220 Microsoft FTP Service
Command:	USER ftp.test.com|anonymous
Response:	331 Anonymous access allowed, send identity (e-mail name) as password.
Command:	PASS 
Response:	230 User logged in.