When I right-clicked on the ClamWin icon in the notification area at the lower, right-hand corner of the screen and selected Open ClamWin, I saw the prompt "You have not yet downloaded Virus Definitions Database. Would you like to download it now?" I chose "Yes" and saw the "Ordinal Not Found" message again.
I saw "Completed" in a "ClamWin Free Antivirus: Download Complete" window,
but when I closed and reopened ClamWin Free Antivirus, I was again informed
that virus definitions had not been downloaded. That occurred even when I
right-clicked on the ClamWin icon in the notifications area and chose
"Exit" and then restarted ClamWin from the directory in which
ClamWin.exe was installed,
C:\Program Files\ClamWin\bin\. Double-clicking on
freshclam.exe in that directory would produce the
"Ordinal Not Found" window.
I tried reinstalling ClamWin and this time was informed that "To complete the installation of ClamWin Free Antivirus, Setup must restart your computer. Would you like to restart now?" I was logged into an administrator account when I updated ClamWin. The user account was also logged in. When I switched to that account prior to rebooting the system, I saw a ClamWin Update window was open with the message "An update of ClamWin Free Antivirus has been released." I now believe that window being open was the cause of the issue I encountered after first installing the update.
I closed that window and logged off the user account. After rebooting the system, ClamWin no longer showed the "Ordinal Not Found" error message and I was able to successfully update the antivirus definitions.