I just checked some of my sitemaps only to find out that for some reason all my sitemaps (that were working just fine before) went into the "ERROR" state.
When researching further I found that I had used <changeFreq> instead of <changefreq> as is listed (now?) in the syntax for sitemaps.
It seems though that Google changed the programming that interprets this xml code only recently, since all my sitemaps were just fine (and no changes were made).
When researching this further on the web, I found that more people that had used uppercase xml code have had issues since end of 10/06. It is possible that I missed this since then.
Make sure to check your maps, and just post a quick message in this thread if you also found that your sitemaps were in the "ERROR" state, and if it was due to the upper/lowercase issue.
Looking at my overall stats, around end of 10/06 my traffic went down as well... Hmmm... Well I'm off to update my sitemaps...