IIS and RSS feeds

Ok, I think this is a different problem than the other rss questions posted so far. I’ve just moved a bunch of wp installations over to a Microsoft OS. I now have two sets of blogs, all with the exact same version of wp (1.5.1.2). The first set remains on the old Linux server with a localhost connection to the database. The other set resides on a Microsoft/IIS server with a remote connection back to the original mysql server. All of the “new” (IIS) blogs are generating feed errors:

1. the feeds validate
2. my feed reader (SharpReader) finds the feeds and subscribes. Everything looks good, until …
3. the first time SharpReader attempts to update, it returns the error: Error reading URL: The underlying connection was closed: The server committed an HTTP protocol violation.

This looks like the dot net upgrade issue, but I thought the wp headers were fixed now. Plus, why doesn’t it generate the error on the first call to the website?

The blogs with the same source files installed on the Linux server do feed to SharpReader just fine. Any thoughts?