You need to give security right to launch and configure excel application to the user who use the excel instance. I think in the case it would be ASPNET user use dcomcnfg tool and search for Microsoft Excel Application on the security tab you can give right to the user. I am using the same kind of application which export the data to excel and i was having same problem. after some playing around this i found out about this. and now all excel process are getting terminated properly. second you need to monitor your code to see if excel generates any error. use try catch finally block to terminate excel instance in all event.