Problem with Feedburner plugin

Hello! I have a question concerning Steve Smith’s Feedburner Replacemnet Plugin. Hopefully those of you who have used it and others who know about it, including Steve himself, might be able to help me.

I am running WP 1.5.2. After installing the plugin, it said that it updated the premalinks structure etc. But when I checked my htaccess (permissions had earlier been set to: 666), it was not written with any rewrite rules.

When I updated the generated URL to the Feedburner setup page, the setup page says:

The URL you entered does not appear to be a valid feed. We encountered the following problem: Error on line 2: The markup in the document following the root element must be well-formed.

And it rejects the setting. So my feedburner is still using my old feed from my old blogger site.

Can someone help me to resolve this? I have also posted at the Feedburner support site but they did not seem to be able to help me. That conversation is found here

TIA!