When you use Internet Explorer 6.0 Service Pack 1 (SP1) to view a MIME type file attachment that is handled by a custom ActiveX control, it may take a long time to view the file, particularly if the file is very large. This behavior is different from what you experience in Internet Explorer 6.0 and earlier in the same scenario.

Internet Explorer 6.0 and earlier versions create an instance of the ActiveX control before the file is downloaded to the cache. However, in Internet Explorer 6.0 SP1, the file is downloaded to the cache immediately -- before an instance of the ActiveX control is created. For performance reasons, this behavior is not optimal, particularly when you view large files. This issue is a side-effect of the hotfix that is described in the following Microsoft Knowledge Base article:

A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This fix may receive additional testing. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next Internet Explorer 6 service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question. The English version of this hotfix has the file attributes (or later) 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
   ------------------------------------------------------
   26-Sep-2003  15:32  6.0.2800.1267  484,352  Urlmon.dll

Note You must reinstall this hotfix after you install the cumulative patch for Internet Explorer that is described in Microsoft Knowledge Base (KB) article 828750.

For additional information, click the following article number to view the article in the Microsoft Knowledge Base: MS03-040: October, 2003, Cumulative Patch for Internet Explorer (828750) After you install this hotfix, the controls that handle the download must set the following DWORD value in the registry to a binary value of 1 under the following registry key: Internet Explorer creates an instance of the control immediately, and then the control can either abort the current download and start a new one or try to bind to the current URL or cache file that is provided.

Microsoft has confirmed that this is a problem in Microsoft Internet Explorer 6 Service Pack 1.

Before the hotfix that is described in Knowledge Base article 310388 is installed, any POST request on a large file that is handled by a custom ActiveX control fails. This issue occurs because Internet Explorer tries to create an instance of the control immediately. Then, it tries to bind to the cache file, but the cache file does not exist because not all the data was downloaded. After you install this hotfix, Internet Explorer downloads the data up front before it creates an instance of the control.