DCOM error shuts down website

We have a web site that keeps shutting down. After restarting IIS Admin service it comes right back up. When it goes down we get the following W3SVC-WP warnings in Event viewer "Applications" and the DCOM error in Event viewer "System":

Event Type:      Warning
Event Source:      W3SVC-WP
Event Category:      None
Event ID:      2237
Date:            12/31/2008
Time:            4:39:51 PM
User:            N/A
Computer:      WEBSVR
Description:
Out of process application '/LM/W3SVC/749866302/Root' terminated unexpectedly.
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Event Type:      Warning
Event Source:      W3SVC-WP
Event Category:      None
Event ID:      2236
Date:            12/31/2008
Time:            4:39:52 PM
User:            N/A
Computer:      WEBSVR
Description:
The server failed to load application '/LM/W3SVC/749866302/Root'.  The error was 'The server process could not be started because the configured identity is incorrect.  Check the username and password.
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Event Type:      Error
Event Source:      DCOM
Event Category:      None
Event ID:      10004
User:      N/A
Computer:      WEBSVR
Description:
DCOM got error "Logon failure: the user has not been granted the requested logon type at this computer. " and was unable to logon .\IWAM_WEB_SVR in order to run the server:
{3D14228D-FBE1-11D0-995D-00C04FD919C1}
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ANy help would be appreciated.