Sitemap error in Google Webmasters

Hi, I'm a very new user. I searched for this but found nothing that was specifically what I've got.

When I submitted a sitemap to Google Webmaster Tools, it seems to be finding links beyond the first 1000. But on that first part of the datafeed, where it ends with "start=1000" there is a large red "X" instead of a green check mark.

Clicking on the part of the datafeed with the "X" to read details of the problem, I get this message:

"Missing XML tag
This required tag is missing. Please add it and resubmit."

It also says this is something related to line "1".

The datafeed in question is not, to my knowledge, an XML datafeed. It's a TAB delimited text file downloaded from CommissionJunction.

I de-registered and removed the datafeed, then uploaded it to the server again and re-registered it in Price Tapestry. Going to the admin page and the merchant page in my PT install, the products are all showing and everything looks fine.

But even after the re-register of the datafeed and the re-submission of the sitemap -- I'm getting the same error for that first part of the sitemap.

Sorry if that's not very clear, I'm on very shaky grounds just learning both price tapestry and sitemaps.

Thanks.

Gary