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Assume that you are connected to one network in Microsoft Internet Security and Acceleration (ISA) Server 2004, and then you try to access a File Transfer Protocol (FTP) server that is connected to a different network. In this scenario, you may experience one of the following symptoms:

  • If you try to use Microsoft Internet Explorer to open a folder that is located on the FTP server, you receive the following error message:

    Windows cannot access this folder. Make sure you typed the file name correctly and that you have permission to access to the folder.

    Details: The operation timed out.

  • If you try to use an FTP client program such as SmartFTP to open a folder that is located on the FTP server, you receive the following error message:

    425 Can't open data connection.


This problem occurs if the following conditions are true:

  • The ISA Server 2004 Firewall Client program is installed and enabled.

  • The Enable folder view for FTP sites check box is selected in Internet Explorer.

    Note If this check box is selected, Internet Explorer exhibits the same behavior as a typical FTP client program. This behavior is described in RFC 959. If this check box is not selected, Internet Explorer sends FTP requests to the Web proxy server as HTTP requests.

    To view RFC 959, visit the following Network Working Group Web site: provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.

  • The Use Passive FTP check box is not selected in Internet Explorer.

    Note This check box controls whether Internet Explorer uses active mode or passive mode FTP.

To locate these check boxes, follow these steps:

  1. Start Internet Explorer.

  2. On the Tools menu, click Internet Options.

  3. Click the Advanced tab, and then under Browsing, locate the following check boxes:

    Enable folder view for FTP sites
    Use Passive FTP

This problem does not occur if the following conditions are true:

  • You use the Ftp.exe command-line FTP client program.

  • The Firewall Client program is not installed, and your computer is configured as a SecureNAT client.


Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.


No prerequisites are required to install this hotfix.

Restart requirement

You do not have to restart your computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.
Date Time Version Size File name
20-Sep-2004 4.0.2161.8573,464 Ftpfltr.dll


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.

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