I figured it out by myself just a few minutes ago. Here is what I did. My Feedburner feed was being transferred from Feedburner to Google and I had to change a cname entry to reflect that change. Everyone knows that changes to the DNS can take up to 48 hours and I first thought that this was the issue.

Other webmasters on various forums reported similar problems, especially those dreaded 404 not found problem. Once the 404 went away I encountered the main problem. The feed was not showing up. When I opened it in the browser it would simply show the Ghacks homepage.

Google support told me to change the url in the Feedsmith WordPress plugin to the new feedproxy url which I did. This did not turn out to fix the initial problem though.

I opened http://feedburner.google.com/, went to the Troubleshootize tab and tried to Resync my feed. Thought that this could be the problem. The resync basically told me that it could not find a feed and that I should check the original feed url at Feedvalidator.

I checked it there and it told me that this was not a valid RSS News Feed. The old url which was entered in Feedburner from day 1 was http://www.ghacks.net/?feed=rss2. You can check that for yourself if you click on the Edit Feed Details tab.

I changed the feed to http://www.ghacks.net/feed which turned out to be a valid feed. The last step was to enter that feed url into the Original Feed option at the Google Feedburner site. I tried to sync the feed and that worked as well. I went to Google Reader and updated my feed and wham, there were all my missing posts.

If you have a similar problem I suggest you check out if your feed in Feedburner ends with ?feed=rss2 or something similar. Check that at Feedvalidator and try other feed urls if the first comes up as no valid RSS News Feed.

Please let me know if you can access my feed properly now. I would also like to hear from other webmasters with the problem.