FormatAccountName exception after logging into Forms site

Question

I've started receiving the following Sharepoint exception whenever I log a user in via Forms Authentication;

Value cannot be null. at Microsoft.SharePoint.Utilities.SPUtility.FormatAccountName(String provider, String user) at Microsoft.SharePoint.Utilities.SPUtility.FormatAccountName(String user) at Microsoft.SharePoint.SPSite.CopyUserToken(SPUserToken userToken) at Microsoft.SharePoint.SPSite.SPSiteConstructor(SPFarm farm, Guid applicationId, Guid contentDatabaseId, Guid siteId, SPUrlZone zone, Uri requestUri, String serverRelativeUrl, Boolean hostHeaderIsSiteName, Uri redirectUri, Pairing pairing, SPUserToken userToken) at Microsoft.SharePoint.SPSite..ctor(SPFarm farm, Uri requestUri, Boolean contextSite, SPUserToken userToken)
at Microsoft.SharePoint.SPSite..ctor(SPFarm farm, Uri requestUri, Boolean contextSite) at Microsoft.SharePoint.WebControls.SPControl.SPWebEnsureSPControl(HttpContext context) at Microsoft.SharePoint.WebControls.SPControl.GetContextWeb(HttpContext context) at Microsoft.SharePoint.ApplicationRuntime.BaseApplication.Application_PreRequestHandlerExecute(Object sender, EventArgs e) at Microsoft.SharePoint.ApplicationRuntime.SPRequestModule.PreRequestExecuteAppHandler(Object oSender, EventArgs ea) at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Can anyone please help me to determine why this is happening or how to prevent it?

Thanks.

Answer 1

you can get some help from here: http://www.sharepointsecurity.com/sharepoint/sharepoint-development/fixing-the-elusive-%E2%80%9Cvalue-cannot-be-null%E2%80%9D-fba-authentication-error/