Google Webmaster Tools returns error for Sitemaps

[info1879]

I've been using XML-Sitemaps without problem for a while but now my submissions come back with this error:

We were unable to read your Sitemap. It may contain an entry we are unable to recognize. Please validate your Sitemap before resubmitting.

[/i]

The sitemaps come back with no errors when tested, and sometimes will say they are submitted if I try a few times. The status of the sitemaps, though, remains as "submitted" and never moves to "indexed." We update our sites daily and resubmit our xml every day so that might be because we submit a new map before it has time to say the old one's been indexed.

Do you have any idea what the parsing error might be and how to correct it? One of my current sitemaps is:

[ External links are visible to forum administrators only ]

The other possibility is that our site is running very slowly right now and I wonder if the webcrawler is just timing out.

[XML-Sitemaps Support]

Hello,

looks like sitemap is rather big and it's possible that googlebot times out when trying to download your sitemap. I would try to enable gzip compression option or set a smaller number of URLs per sitemap file to make a set of smaller files.