ReportServer application pool stopped with unspecified error and keeps crashing giving 1057 and 1059 errors

Today ran into a SCOM Report Server that would not load correctly on a Windows 2003 with SQL 2005 version.
This also gives an error in SCOM console as follows:
Data Warehouse failed to request a list of management packs from SQL RS server..
And in the description a reference to:
The request failed with HTTP status 503: Service Unavailable.
When connecting to http://reportserver/reports it just displays a Service Unavailable message.
We quickly enough saw that the ReportServer application pool in the report server was not running. When starting the application pool from the IIS manager it start correctly. However when the first connection was made to http://reportserver/reports or /reportserver we got an error and the application pool had been stopped. The application pool was Stopped and had unspecified error when looking at it from the IIS manager.
We got the following two errors in the event viewer on the report server in the System log.

We tried to reset the password on the application pool. Did not work. We tried to set the account back to network service in the Report Server configuration tool and after a restart of the reportserver set it back. We confirmed we were using the right password.
When looking through the local rights I noticed the account was not in the IIS_WPG group on that machine.
Added the account we were running the application pool as to that group.
Got error again.
Did an IISRESET from the command line.
Success! B)
So this solved my issue and we could move on to the next step. The SCOM alert auto closed right after this. Good times!
By the way:
I did find a link to a solution in the case you are running many application pools on one web server (about 60 or more). It tells you to create a regkey UseSharedWPDesktop and set it as stated in this document:
This did not apply to our environment as it was a dedicated machine.
Bob Cornelissen