When someone logs in to my site i get a critical error message on the home page and the following message in the system log (page exception error). This has started after enabling OpenID and LiveID to the login options.

I tested the system by changing the page that the login goes to but it keeps sending me back to my home page. Please can someone point me in the direction i need to go as cannot find a reason for this error?

Error message:

AssemblyVersion: 05.00.00
PortalID: 0
PortalName: Termite Nation
UserID: -1
UserName:
ActiveTabID: 38
ActiveTabName: Home
RawURL: /Home/tabid/38/ctl/Login/Default.aspx?returnurl=%2fHome%2ftabid%2f38%2fDefault.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.termitenation.com/Home/tabid/38/ctl/Login/Default.aspx?returnurl=%2fHome%2ftabid%2f38%2fDefault.aspx
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.9.0.11) Gecko/2009060215 Firefox/3.0.11 (.NET CLR 3.5.30729)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 9400b673-c259-4608-bf99-32d23402a1b1
InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.Common.Utilities.XmlUtils.GetAttributeValueAsInteger
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Common.Utilities.XmlUtils.GetAttributeValueAsInteger(XPathNavigator nav, String AttributeName, Int32 DefaultValue) at DotNetNuke.Common.Utilities.Config.GetPersistentCookieTimeout() at DotNetNuke.Entities.Users.UserController.UserLogin(Int32 portalId, UserInfo user, String PortalName, String IP, Boolean CreatePersistentCookie) at DotNetNuke.Modules.Admin.Authentication.Login.ValidateUser(UserInfo objUser, Boolean ignoreExpiring) at DotNetNuke.Modules.Admin.Authentication.Login.UserAuthenticated(Object sender, UserAuthenticatedEventArgs e) at DotNetNuke.Services.Authentication.AuthenticationLoginBase.OnUserAuthenticated(UserAuthenticatedEventArgs ea) at DotNetNuke.Modules.Admin.Authentication.Login.cmdLogin_Click(Object sender, EventArgs e) at System.Web.UI.WebControls.Button.OnClick(EventArgs e) at System.Web.UI.WebControls.Button.RaisePostBackEvent(String EVENT_ARGUMENT) at System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String EVENT_ARGUMENT) at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String EVENT_ARGUMENT) at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---
Source:

 I ran a comparison of the web.config files from the current setup with a file i had backed off a few days earlier and found that part of the file had changed. I restored the sections of the config file that had changed and the login started to work again without error.

I ran several tests installing the live and open id options but this did not change the web.config as before. 

I then looked at my host which runs a Plesk control panel and found that there is an option to select authenticiation, now changing this from form to window and back again it causes the web.config to corrupt.

the web.config file loses a chunk of data..

<!-- forms or Windows authentication -->

 <authentication mode="forms"> <forms name=".DOTNETNUKE" protection="All" timeout="60" cookieless="UseCookies" /> </authentication> <!-- <identity impersonate="true"/>

becomes

<!-- forms or Windows authentication -->

<!-- <identity impersonate="true"/>

This causes a critical error just after logging in to the site (you can still log in) and this error disappears when you switch page, however what it does is that it stops you nominating a page to go to after login (will default to the home page).

Even without host programs making those kind of changes, I have run into web.config problems several times now over the last few years.  It seems that every time a new version of DNN is released, they re-arrange the web.config file that goes along with it dramatically.  Sometimes they merely change the formatting and order of entries(which make it difficult to find the changes), but sometimes they add/remove important parts. 

This is quite often the most overlooked cause of problems with DNN, and why I now make it a habit of using the release.config file that comes with each new version, only importing the very barest of essentials to make it work with my server, instead of just upgrading and hoping for the best.