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Source: Microsoft Support
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When you use the address bar of Internet Explorer 6.0 or later to enter a username and password to access an FTP site, and the format of the URL you enter is ftp://username:password@domain, the following error message is displayed:
Windows cannot find ' ftp://username:password@domain'. Check the spelling and try again.
Either the username or the password contains any one of the characters:
: # ? / \ %
This behavior is by design.
If the username or password needs to contain any one of the characters listed in the Cause section, you will need to encode the special characters in the following way:
# -> %23
/ -> %2F
: -> %3A
? -> %3F
\ -> %5C
% -> %25
Consider the following example.
A user with the username "jdoe" and a password of "Sure?" who wants to access an FTP site on a server called "ftpserver".
When the user tries to access the site using Internet Explorer and enters ftp://jdoe:Sure?@ftpserver into the address bar, the access will fail and the error message described above will be displayed.
However, when the user enters ftp://jdoe:Sure%3F@ftpserver in the address bar, he or she will successfully access the FTP server.
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