Pingback problems with WordPress 2.0.4 and IIS

I have installed WordPress 2.0.4 with PHP 5.1.4 and MySQL 5.0.21 on Windows 2003 Server with IIS 6.0. I am using the PATH_INFO method for permalinks (index.php is embedded in the permalink). I have not installed a mod_rewrite module.
There are two blogs on my webserver, trackbacks between them work, but pingbacks do not.
The default for discussions is to allow comments and pings. The only restriction on comment posting is that an admin must approve.
Both blogs use the Default 1.6 WordPress theme.
I turned on $xmlrpc_logging in xmlrpc.php on both blogs, on the receiving blog, there are log entries like this:
BEGIN ENTRY from xmlrpc.log:
2006-08-10 17:41:08 Input: <?xml version=”1.0″?>
<methodCall>
<methodName>pingback.ping</methodName>
<params>
<param><value><string>http://testwp.sals.edu/index.php/2006/08/10/internal-pingback-test/</string></value></param&gt;
<param><value><string>http://testblogc.sals.edu/index.php/2006/08/10/hello-world/</string></value></param&gt;
</params></methodCall>

2006-08-10 17:41:08 Output: (PB) URI=’http://testblogc.sals.edu/index.php/2006/08/10/hello-world/&#8217; ID=’2006′ Found=’from the path’
END ENTRY from xmlrpc.log

So, I think the ping is getting to the receiving log, but pingbacks do not appear.

(I also have IIS logs but they are too large to post here.)
Any ideas what could be preventing pingbacks from appearing?