What could be causing this all of a sudden?

Webmaster tools has shown no errors at all for a few weeks and now this. Nothing on our server or with the setup has been changed since then. What's the scoop?

Click on the sitemap file and get more details about what the error is. The screen doesn't help

When I click on the red X links to get more info, I get:

e Status Details - We encountered an error while trying to access your Sitemap. Please ensure your Sitemap follows our guidelines and can be accessed at the location you provided and then resubmit.

Delete all sitemap xml.gz files in /data/
and re-run manually.

Make sure it actually completes the build with no errors reported.

Done that. Now should I resubmit to Google in Webmaster tools?

It will pick it up automatically, but it can't hurt to resubmit. The idea here was to make sure it was fully completing.

It happened again today according to webmaster tools:

Error: The last attempt at downloading the Sitemap failed. The details below are representative of the last successful download. Resubmit?
See Sitemap
Format URLs in Sitemap Submitted Downloaded Sitemap Total: 20,000, Indexed: 585 Oct 25, 2009 – Error
Nov 28, 2009 Sitemap errors and warnings

Line Status Details - We encountered an error while trying to access your Sitemap. Please ensure your Sitemap follows our guidelines and can be accessed at the location you provided and then resubmit. Problem detected on: Nov 28, 2009

It doesn't appear that this is a problem with the sitemap, but more likely a problem with Google. I say this only because I am using vb4 b4's built in sitemap generator and started receiving the exact problem yesterday. I submitted a vB bug but think I will cancel it based on the research I have done. The file's in all cases appear fine but google seems them as blank. The weird thing is if I try to view the sitemap through a browser I get an error there. But if I download it and view it, it opens fine. Does the same occur for you using vbseo sitemap?

Originally Posted by tribedude

It happened again today according to webmaster tools:

Error: The last attempt at downloading the Sitemap failed. The details below are representative of the last successful download. Resubmit?
See Sitemap
Format URLs in Sitemap Submitted Downloaded Sitemap Total: 20,000, Indexed: 585 Oct 25, 2009 – Error
Nov 28, 2009 Sitemap errors and warnings

Line Status Details - We encountered an error while trying to access your Sitemap. Please ensure your Sitemap follows our guidelines and can be accessed at the location you provided and then resubmit. Problem detected on: Nov 28, 2009

Your sitemap is working, that's should something on google bots can not download your sitemap in this time. just resubmit it again and it should work

Re-submitting the sitemap results in the same errors.

Check that your host isn't blocking google bot.

No, I don't think that is it either. If I try to view the sitemap in a browser I get an error that way:
http://www.kyrivalry.com/forums/site...d_1_394.xml.gz

The XML page cannot be displayed

Cannot view XML input using style sheet. Please correct the error and then click the Refresh button, or try again later. XML document must have a top level element.

Google is getting the Index and Forum xml fine, but not the Thread xml. I wonder if something has changed with the urlset tag or something?

Sorry, but we do not support vb4's sitemap.

Yes I understand that and wasn't looking for support as much as I was looking for a discussion about the sitemap problem; specifically because it doesn't seem to be a problem with vbulletin's or vbseo's sitemap since both users are experiencing the same problem.