Symptoms
After you install or upgrade to Microsoft Exchange Server 2019 Cumulative Update (CU) 8, you receive error messages that resemble the following in computers event log:
Log Name: Application Source: ASP.NET 4.0.30319.0 Event ID: 1309 Task Category: Web Event Level: Warning Keywords: Classic Description:
Exception information: Exception type: DuplicateKeyException Exception message: Cannot add a duplicate key. Use Insert instead at Microsoft.Exchange.Security.Authentication.FederatedAuthService.CacheReader.AddEntry(String userKey, Int32 userPolicy, ConfigWrapper config)
or
Log Name: Application Source: MSExchange Common Event ID: 4999 Task Category: General Level: Error Keywords: Classic Description:
Watson report about to be sent for process id: 3292, with parameters: E12IIS, c-RTL-AMD64, 15.02.0659.004, w3wp#MSExchangePowerShellFrontEndAppPool, M.Exchange.Security, M.E.S.A.F.CacheReader.AddEntry, M.E.C.TimeoutCache.DuplicateKeyException, 28e2-dumptidset, 15.02.0659.004. ErrorReportingEnabled: True
or
Log Name: Application Source: MSExchange Front End HTTP Event ID: 1003 Task Category: Core Level: Error Keywords: Classic Description:
[PowerShell] An internal server error occurred. The unhandled exception was: Microsoft.Exchange.Collections.TimeoutCache.DuplicateKeyException: Cannot add a duplicate key. Use Insert instead at Microsoft.Exchange.Security.Authentication.FederatedAuthService.CacheReader.AddEntry(String userKey, Int32 userPolicy, ConfigWrapper config) at Microsoft.Exchange.Security.Authentication.FederatedAuthService.BasicAuthPolicyRepo.GetUserPolicy(String userKey, Int32 traceId, Int32& userPolicy, HttpApplication httpApplication, IRecipientSession recipientSession, IConfigurationSession configSession, ConfigWrapper config) at Microsoft.Exchange.Security.Authentication.FederatedAuthService.BasicAuthPolicyEvaluator.IsBasicAuthAllowed(String userKey, String protocolName, Int32 traceId, HttpApplication httpApplication, IRecipientSession recipientSession, IConfigurationSession configSession, ConfigWrapper config) at Microsoft.Exchange.HttpProxy.ProxyModule.IsLegacyAuthAllowed(HttpApplication httpApplication) at Microsoft.Exchange.HttpProxy.ProxyModule.OnPostAuthenticateInternal(HttpApplication httpApplication) at Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate, Func`2 filterDelegate, Action`1 catchDelegate)
Cause
This issue is caused by an internal change applied in Exchange Server 2019 CU8. You can safely ignore these event log entries now. The behavior will be addressed with a later update.
Resolution
To fix this issue, install the Cumulative Update 9 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.
Workaround
Users could be prompted for credentials for Outlook when receiving the DuplicateKeyException error that's described in the Symptoms section. You can run the following command to revert the change that was made in CU8:
Set-OrganizationConfig -DefaultAuthenticationPolicy $null
