Google Base XML file format

I am trying to prepare a XML file for uploading to Google Base (www.google.com/base) , but am not having much luck. Below is a snippet of the code I have been using. The error message I get is "Data feed upload failed. No items are live."

I cant find an example of a full working XML file that I know works on Google base to follow. So am unsure what I am doing wrong. Perhaps I should be using some header and footer commands or code that I have omitted? Perhaps I need to place the attributes in a particular order?

Can anyone suggest what I might do?

Very many thanks

<item>
<g:price>24.20</g:price> <g:currency>GBP</g:currency>
<link>http://www.myurl.com/mypage.php?myid=mynumber</link>
<g:id>MYNUMBER</g:id>
<title>My Title Here</title>
<g:image_link>http://www.myurl.com/course_image_2.jpg</g:image_link>
<description>My Description Here</description>
<g:payment_accepted>Visa</g:payment_accepted> 
<g:payment_accepted> MasterCard</g:payment_accepted> 
<g:payment_accepted> Discover</g:payment_accepted> 
<g:payment_accepted> Discover</g:payment_accepted> 
<g:payment_accepted> AmericanExpress</g:payment_accepted> 
<g:payment_notes> PayPal accepted</g:payment_notes>
</item>

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