Strange behaviour from web.config

Hi,

I have a web service running in Window 2003 that make some call to a DCOM. As default, ASP.NET doesn't have any permission to execute a DCOM. To enabled that, I add in a <identity> tag to impersonate an account that has the permission to execute DCOM. Instead of put in a clear text username/password, I have used aspnet_setreg tool to encrypt username/password and stored in registry.

The issue here is that once I called the web service, other user that call this web service will hit an error in web.config saying failure when read pasword from registry. But strange enough, after left the web service idle for some times, another user can made a call to this web service and in return, cause other users and myself to hit that error.

Does anyone has any idea what causing this strange behaviour