Anonymous user when subscribing to RSS feeds for a List on an Internet facing site throws “An unexpected error has occurred”

I have an Internet facing SharePoint 2010 site collection which has anonymous access enabled, the list is set to view items for anonymous users. The anonymous users can view the list, but when you click on the RSS link it throws the infamous SharePoint error“An unexpected error has occurred”

e.g. Site URL http://www.myInternetSite.com

List URL: http://www.myinternetsite.com/subsite/lists/Posts/AllPosts.aspx

Feed URL: http://www.myinternetsite.com/SafetyAlerts/_layouts/listfeed.aspx?List{GUID}&Source=http%3A%2F%2Fwww.myinternetsite.com

From the ULS logs this what I found:

System.FormatException:Inputstring was notin a correct format.
 at System.Number.StringToNumber(String str,NumberStyles options,NumberBuffer&     number,NumberFormatInfo info,Boolean parseDecimal)
 at System.Number.ParseInt32(String s,NumberStyles style,NumberFormatInfo info)
 at Microsoft.SharePoint.SPChangeToken.ParseChangeToken(String strChangeToken)
 at Microsoft.SharePoint.SPChangeToken..ctor(String strChangeToken)
 at Microsoft.SharePoint.ApplicationPages.ListFeed.get_NeedToFetchItems()
 at Microsoft.SharePoint.ApplicationPages.ListFeed.OnPreInit(EventArgs e)
at System.Web.UI.Page.PerformPreInit()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint,Boolean includeStagesAfterAsyncPoint

Now internally on the network, the anonymous site works and the users can subscribe to the list RSS without the need for users to authenticate. We are behind a proxy server and this has been added to bypass in the web.config.

The internet site available over also site behind a firewall but the only exception being the users cannot authenticate if the request comes from outside of our network.