Hi,This is our Exchange enviorment setup:(one) Exchange Server 2007 SP1 rollup 5. Running on a Windows Server 2003 R2 SP2.I don't really have any users reporting any problems regarding email. But looking in the Application Event Log I see alot of the following warnings: Event Type:WarningEvent Source:MSExchange Web ServicesEvent Category:Core Event ID:5Date:2009-02-27Time:19:57:49User:N/AComputer:MY-SERVERDescription:Unable to send a notification for subscription HQBhd3N0b3NydjA1LmFjYWRlbWljd29yay5sb2NhbBAAAACykwfyGuuJSIrp5cV7B8Ie. Will retry.and also someEvent Type:ErrorEvent Source:MSExchange Web ServicesEvent Category:Core Event ID:7Date:2009-02-27Time:19:48:45User:N/AComputer:MY-SERVERDescription:After 6 unsuccessful attempts to send a notification for subscription HQBhd3N0b3NydjA1LmFjYWRlbWljd29yay5sb2NhbBAAAADczwfjcr+2Ro5T0tq3t6bE, subscription has been removed.I don't find much info on this one out there. So i really hope you guys can help me figure out what might be causing this :)RegardsErik

Hi,Not sure I follow you Gregory :)Which user doesn'tExchange Web Servicesimpersonate? And when does Exchange need toimpersonate that user?We only haveone custom third party web application in the IIS on the Exchange server. Since it's not we who developed it I am not sure what kind of calls it makes. But what the application does is to sync meetings in the Outlook 2007 calendar with our management system for the phones.Does that sound like an application that could cause this kind of warnings?// Erik

We're having this same problem in our Exchange environment, and in our case, it seems to be originating from Alert subscriptions within Project Server. The alerts are actually coming through, however, and tasks and appointments are being created appropriately so impersonation is working, but Exchange is not receiving an ACK response on the subscription notifications, and thus continues retrying. I have also noticed a plethora of 401.2.2148074254 errors in the IIS logs. Any advice?