My user can't connect some mailbox in same time

My user have issue can't connect mailbox. But after about 10 - 15 minutes everything is comeback to normal. In same time other user can connect mailbox. Please help to recommend about the solution for fix this issue.

Error in time have issue....... See under line

Request
Url:https://webmail.xxxxx.com:443/owa/auth.owa
User host address:xxxxxxx
OWA version:14.1.255.0

Exception
Exception type: System.InvalidOperationException
Exception message: Operation is not valid due the current state of the object.

Call stack
Microsoft.Exchange.Data.Storage.ExchangePrincipal.get_ServerFullyQualifiedDomianName()
Microsoft.Exchange.Clients.Owa.Core.ProxyUtilities.GetMailboxInfo(ExchangePrincipal exchangePrincipal, Site& targetSite, Site& currentSite, Serverversion& targetversion)
Microsoft.Exchange.Clients.Owa.Core.ProxyUtilities.NeedOnsiteLegacyRedirect(ExchangePrincipal exchangePrincipal, Configuration, Uri& legacyRedirectUrl, Boolean& HttpApplication httpApplication)
Microsoft.Exchange.Clients.Owa.Core.FBASingleSignOnFilterChain.HandleIfLegacyRedirect(WindowsIdentity identity, String explicitLogonUser, Configuration owaconfiguration, HttpApplication httpApplication)
Microsoft.Exchange.Clients.Owa.Core.FBASingleSignOnFilterChain.FilterRequest(Object source, EventArgs e, RequestEventType eventType)
Microsoft.Exchange.Clients.Owa.Core.RequestFilterChain.ExexcuteRequestFilterChain(Object source, EventArgs e, RequestEventType eventType)
Microsoft.Exchange.Clients.Owa.Core.OwaReuestEventInspector.OnpostAuthorizeRequest(Object sender, EventArgs e)
System.Web.HttpApplication.SyncEventExcecutionStep.System.Web.HttpApplication,IExecutionStep.Execute()
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Thanks in advance.