I just typed a huge response and FF crashed and I lost it I hate it when that happens!!
Basically its possible to have two sites with different content, one running under www. and one without the www a bit like a subdomain. Because of this when you submitted your sitemap google sees its on the www site (http://www.appsamuck.com/sitemap.xml) but all the urls in your sitemap do not contain the www, therefore google is wondering if the sitemap is actually for another site the non www section. Usually these two deliver the same content but not always, so google is saying hang on you put the sitemap at www, but all your pages are on a non www domain whats that about!!
The best thing to do is stick to one or the other, are you advertising the www or non www? Whichever you are using (and I suggest the www version), submit your sitemap with www and make sure all your urls in your sitemap have www in them. That way google wont throw a fit. Also sticking to one may be slightly better for SEO.
As Nick suggested above, its also a good idea to let google know which one you prefer through the preferred domain option. I would set this option
Display URLs as www.appsamuck.com (for both www.appsamuck.com and appsamuck.com)
At least google will know that your talking about the same site then.
As for the sitemap, well there are some issues with that too.
Firstly as I pointed out about its missing the www from each URL.
Secondly you are missing an xml declaration etc for the top of the file. YOu need something like this
print("code sample");<?xml version="1.0" encoding="UTF-8"?>
<urlset
xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9
http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">
Like Diodeus above suggested you really should add the other fields in such as priority etc.
Here is a quick go I have done for you (note it follows on from the above as I have opened the urlset tag above and it closes at the bottom of this set of code)
print("code sample");
<url>
<loc>http://www.appsamuck.com/</loc>
<priority>1.00</priority>
<lastmod>2008-10-17T03:01:05+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/index.html</loc>
<priority>0.80</priority>
<lastmod>2008-10-17T03:01:05+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/blog/</loc>
<priority>0.80</priority>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/about.html</loc>
<priority>0.80</priority>
<lastmod>2008-10-16T00:00:32+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/contact.html</loc>
<priority>0.80</priority>
<lastmod>2008-10-16T00:00:33+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/iphonesdkdev.html</loc>
<priority>0.80</priority>
<lastmod>2008-10-14T05:41:03+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/day16.html</loc>
<priority>0.80</priority>
<lastmod>2008-10-17T03:13:21+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/day15.html</loc>
<priority>0.80</priority>
<lastmod>2008-10-16T15:58:57+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/day14.html</loc>
<priority>0.80</priority>
<lastmod>2008-10-15T16:58:06+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
<url>
<loc>http://www.appsamuck.com/day13.html</loc>
<priority>0.80</priority>
<lastmod>2008-10-13T17:52:08+00:00</lastmod>
<changefreq>monthly</changefreq>
</url>
</urlset>
Its not a full list im not going to do all the work for you :)
There are also some good online tools that will create sitemaps for you, they crawl the site and build it, just google xml-sitemaps and you should find some, there are some good free ones. Also if their spider cannot find your content its a flag that google probably cannot either,so it has a dual purpose.
Hope that helps :)
Paul