I installed Plesk on 64-bit version of Windows Server 2003. But all my sites fail with
`Service Unavailable`
How this can be fixed?
RESOLUTION

The source of this problem is in IIS works in 64-bit mode by default. The problems related to IIS functionality in 64-bit mode are described in the following article:

http://support.microsoft.com/?id=895976

IIS 6.0 supports both the 32-bit mode and the 64-bit mode. However IIS 6.0 does not support running both modes at the same time on a 64-bit version of Windows.

1.
To switch IIS to 32-bit mode use the following command:

cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 1
2.
To switch IIS back to 64-bit mode use the following command:

cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 0

Keywords: Could not load ISAPI 64-bit 32-bit mode IIS