Normally ASP.Net does not have the required privileges to create an event log source, so you have to create one manually, or execute the creation code with the required privileges.
To sort out this little problem, there is a command line utility included in Windows called eventcreate. I've NEVER heard of this before, but apparently it has existed for a long time. It actually creates an event, but will create the specified event log source if called with the correct priviliges, like the Administrator account.
eventcreate /SO "MyApp" /D "MyMessage" /L Application /T ERROR /ID 999
SUCCESS: A 'ERROR' type event is created in the 'MyApp' log/source.
